There are several one-per-planet and Super Project improvements that, when you upgrade them, can be build again. For example, a second Colonial Hospital can be build, if you upgrade the first one to a Xeno Medical Center. Same for the Outreach Group, if you upgrade it to a Mediation Center. I believe this is because the Preclusions-tag for those improvements isn't correctly set to preclude the previous versions. I've went through the ImprovementDefs.xml, and made a list of all affected improvements, what their Preclusions-tag currently says, and what it should say. Warning, this list is long.
SolarPowerPlant:
<Preclusions>
<Improvement>QuantumPowerPlant</Improvement>
<Improvement>PracticalFusion</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>FusionPowerPlant</Improvement>
<Improvement>AntimatterPowerPlant</Improvement>
<Improvement>QuantumPowerPlant</Improvement>
</Preclusions>
FusionPowerPlant:
<Preclusions>
<Improvement>QuantumPowerPlant</Improvement>
<Improvement>SolarPowerPlant</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>SolarPowerPlant</Improvement>
<Improvement>AntimatterPowerPlant</Improvement>
<Improvement>QuantumPowerPlant</Improvement>
</Preclusions>
AntimatterPowerPlant:
<Preclusions>
<Improvement>QuantumPowerPlant</Improvement>
<Improvement>SolarPowerPlant</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>SolarPowerPlant</Improvement>
<Improvement>FusionPowerPlant</Improvement>
<Improvement>QuantumPowerPlant</Improvement>
</Preclusions>
QuantumPowerPlant:
<Preclusions>
<Improvement>AntimatterPowerPlant</Improvement>
<Improvement>SolarPowerPlant</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>SolarPowerPlant</Improvement>
<Improvement>FusionPowerPlant</Improvement>
<Improvement>AntimatterPowerPlant</Improvement>
</Preclusions>
InnovationComplex:
<Preclusions>
<Improvement>OmegaResearchCenter</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>ResearchCoordinationCenter</Improvement>
<Improvement>OmegaResearchCenter</Improvement>
</Preclusions>
OmegaResearchCenter:
<Preclusions>
<Improvement>InnovationComplex</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>ResearchCoordinationCenter</Improvement>
<Improvement>InnovationComplex</Improvement>
</Preclusions>
FoodDistribution:
<Preclusions>
<Improvement>XenoIrrigation</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>XenoIrrigation</Improvement>
<Improvement>BiomassResequencer</Improvement>
</Preclusions>
XenoIrrigation:
<Preclusions>
<Improvement>BiomassResequencer</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>FoodDistribution</Improvement>
<Improvement>BiomassResequencer</Improvement>
</Preclusions>
BiomassResequencer:
<Preclusions>
<Improvement>XenoIrrigation</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>FoodDistribution</Improvement>
<Improvement>XenoIrrigation</Improvement>
</Preclusions>
XenoMedicalCenter:
<Preclusions>
<Improvement>FertilityCenter</Improvement>
<Improvement>ReplicationCenter</Improvement>
</Preclusions>
should be
Preclusions>
<Improvement>ColonialHospital</Improvement>
<Improvement>FertilityCenter</Improvement>
<Improvement>ReplicationCenter</Improvement>
</Preclusions>
FertilityCenter:
<Preclusions>
<Improvement>XenoMedicalCenter</Improvement>
<Improvement>ReplicationCenter</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>ColonialHospital</Improvement>
<Improvement>XenoMedicalCenter</Improvement>
<Improvement>ReplicationCenter</Improvement>
</Preclusions>
ReplicationCenter:
<Preclusions>
<Improvement>XenoMedicalCenter</Improvement>
<Improvement>FertilityCenter</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>ColonialHospital</Improvement>
<Improvement>XenoMedicalCenter</Improvement>
<Improvement>FertilityCenter</Improvement>
</Preclusions>
Embassy:
<Preclusions>
<Improvement>DiplomaticMinistry</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>DiplomaticDistrict</Improvement>
<Improvement>DiplomaticMinistry</Improvement>
</Preclusions>
DiplomaticDistrict:
<Preclusions>
<Improvement>Embassy</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>Embassy</Improvement>
<Improvement>DiplomaticMinistry</Improvement>
</Preclusions>
DiplomaticMinistry:
<Preclusions>
<Improvement>Embassy</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>Embassy</Improvement>
<Improvement>DiplomaticDistrict</Improvement>
</Preclusions>
CulturalCenter:
<Preclusions>
<Improvement>OutreachCenter</Improvement>
<Improvement>EmigrationCenter</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>Consulate</Improvement>
<Improvement>OutreachCenter</Improvement>
<Improvement>EmigrationCenter</Improvement>
</Preclusions>
OutreachCenter:
<Preclusions>
<Improvement>CulturalCenter</Improvement>
<Improvement>EmigrationCenter</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>Consulate</Improvement>
<Improvement>CulturalCenter</Improvement>
<Improvement>EmigrationCenter</Improvement>
</Preclusions>
EmigrationCenter:
<Preclusions>
<Improvement>CulturalCenter</Improvement>
<Improvement>OutreachCenter</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>Consulate</Improvement>
<Improvement>CulturalCenter</Improvement>
<Improvement>OutreachCenter</Improvement>
</Preclusions>
Bank:
<Preclusions>
<Improvement>FinancialSector</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>BankingSector</Improvement>
<Improvement>FinancialSector</Improvement>
</Preclusions>
BankingSector:
<Preclusions>
<Improvement>FinancialSector</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>Bank</Improvement>
<Improvement>FinancialSector</Improvement>
</Preclusions>
FinancialSector:
<Preclusions>
<Improvement>Bank</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>Bank</Improvement>
<Improvement>BankingSector</Improvement>
</Preclusions>
TradeCenter:
<Preclusions>
<Improvement>CustomsOffice</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>TradePost</Improvement>
<Improvement>CustomsOffice</Improvement>
</Preclusions>
CustomsOffice:
<Preclusions>
<Improvement>TradeCenter</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>TradePost</Improvement>
<Improvement>TradeCenter</Improvement>
</Preclusions>
Stadium:
<Preclusions>
<Improvement>AmusementPark</Improvement>
<Improvement>MegaResort</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>EntertainmentNetwork</Improvement>
<Improvement>AmusementPark</Improvement>
<Improvement>MegaResort</Improvement>
</Preclusions>
AmusementPark:
<Preclusions>
<Improvement>Stadium</Improvement>
<Improvement>MegaResort</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>EntertainmentNetwork</Improvement>
<Improvement>Stadium</Improvement>
<Improvement>MegaResort</Improvement>
</Preclusions>
MegaResort:
<Preclusions>
<Improvement>Stadium</Improvement>
<Improvement>AmusementPark</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>EntertainmentNetwork</Improvement>
<Improvement>Stadium</Improvement>
<Improvement>AmusementPark</Improvement>
</Preclusions>
TouristHaven:
<Preclusions>
<Improvement>TouristDestination</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>PortofCall</Improvement>
<Improvement>TouristDestination</Improvement>
</Preclusions>
TouristDestination:
<Preclusions>
<Improvement>TouristHaven</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>PortofCall</Improvement>
<Improvement>TouristHaven</Improvement>
</Preclusions>
SlaveMill:
<Preclusions>
<Improvement>SlaveFactory</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>SlavePit</Improvement>
<Improvement>SlaveFactory</Improvement>
</Preclusions>
SlaveFactory:
<Preclusions>
<Improvement>SlaveMill</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>SlavePit</Improvement>
<Improvement>SlaveMill</Improvement>
</Preclusions>
Arena:
<Preclusions>
<Improvement>Slaughtertorium</Improvement>
<Improvement>HuntingGrounds</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>FightingPit</Improvement>
<Improvement>Slaughtertorium</Improvement>
<Improvement>HuntingGrounds</Improvement>
</Preclusions>
Slaughtertorium:
<Preclusions>
<Improvement>Arena</Improvement>
<Improvement>HuntingGrounds</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>FightingPit</Improvement>
<Improvement>Arena</Improvement>
<Improvement>HuntingGrounds</Improvement>
</Preclusions>
HuntingGrounds:
<Preclusions>
<Improvement>Arena</Improvement>
<Improvement>Slaughtertorium</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>FightingPit</Improvement>
<Improvement>Arena</Improvement>
<Improvement>Slaughtertorium</Improvement>
</Preclusions>
HealingPools:
<Preclusions>
<Improvement>CommunionShrine</Improvement>
<Improvement>MeditationCenter</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>MeditationCenter</Improvement>
<Improvement>CommunionShrine</Improvement>
<Improvement>DrathianTemple</Improvement>
</Preclusions>
MeditationCenter:
<Preclusions>
<Improvement>CommunionShrine</Improvement>
<Improvement>Healing Pools</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>HealingPools</Improvement>
<Improvement>CommunionShrine</Improvement>
<Improvement>DrathianTemple</Improvement>
</Preclusions>
CommunionShrine:
<Preclusions>
<Improvement>MeditationCenter</Improvement>
<Improvement>Healing Pools</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>HealingPools</Improvement>
<Improvement>MeditationCenter</Improvement>
<Improvement>DrathianTemple</Improvement>
</Preclusions>
IridiumStore:
<Preclusions>
<Improvement>IridiumCenter</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>IridiumCenter</Improvement>
<Improvement>IridiumWorld</Improvement>
</Preclusions>
IridiumCenter:
<Preclusions>
<Improvement>IridiumWorld</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>IridiumStore</Improvement>
<Improvement>IridiumWorld</Improvement>
</Preclusions>
IridiumWorld:
<Preclusions>
<Improvement>IridiumCenter</Improvement>
</Preclusions>
should be
<Preclusions>
<Improvement>IridiumStore</Improvement>
<Improvement>IridiumCenter</Improvement>
</Preclusions>
ElevationFoundation:
doesn't have the tag at all, should be
<Preclusions>
<Improvement>MissionaryCenter</Improvement>
</Preclusions>
MediationCenter:
doesn't have the tag at all, should be
<Preclusions>
<Improvement>OutreachGroup</Improvement>
</Preclusions>
CitadelofRepression:
doesn't have the tag at all, should be
<Preclusions>
<Improvement>IntimidationCenter</Improvement>
</Preclusions>