First and most important I am enjoying the game immensely, well done.
I am around turn 500. Under the Victory Tab, I click on Influence Victory. The button on the left states I have 64% at this time. The window that opens states I need 76% to win which I believe agrees with the manual. Also in the window now open it states I need 21% more to win. Obviously, 64% plus 21% is more than the 76% shown.
I have been pushing for an Influence Victory for a number of turns. Under the Govern tab and Timeline tab if I strike Influence, I get the graph showing influence over time. The graph shows all the players flat lined with no change in influence since around turn 440. I know it has changes since I have been pushing hard for a influence victory for the last 100 turns.
Along those lines, I was at 76% a few turns ago and it suddenly dropped down to 64%. This could very well be due to one of my opponents reacting to my coming close to an influence victory.