I think you saved the games on version 0.75 (the one with the Advent), and now they made a rollback to version 0.62 (the one with just the TEC factions), which saved the games in a different directory.
See this post, to check what are the folders used by the different versions (these folders are for Windows 7, in other OS' they should be very similar):
https://forums.sinsofasolarempire.com/420818
Still, I don't think you are going to be able to use the saved games, at least not, until they reactivate version 0.75 again, but who knows, maybe they will.
Hope this helps!