Can Board decide to increase size from 3 to 5?

The language you cite gives the board the authority to increase the size; it doesn't give the president that authority.

The board vote to increase should have been part of the meeting minutes. It wouldn't necessarily be in any other document. At the time of the increase, didn't the board appoint two new directors? That would be in the minutes too.

Are you on the board? Do you want it to be a different size? I'm curious why this past president's (mis?)behavior interests you.

Since you don’t have access to the records of six years ago it will be difficult to prove that the change from 3 to 5 members wasn’t properly done. If as you allege that it was done by a previous president because: This makes me think he choose to increase the board size without any approval as he was in constant conflict with original board members. It seems to me that the two Board members that he didn’t agree with would have / should have raised the issue that it was improper at the time.

But back to Carol’s question: What are you looking to do? If you want to return the Board to only three people because of some procedural error six years ago then it would be simple for the current BOD to pass a resolution expanding it back to five.

As to the concerns you posed in your second post it sounds to me more like sour grapes than anything. You were Board president but resigned because the rest of the Board didn’t agree with you, instead of fighting to do things right if they were indeed being done wrong, you instead chose to take your ball and go home. While it is true that as president you only had one vote like every other director but you had the bully pulpit; you had the power to shine the light on any improprieties.

You still have that power although it will be harder now by talking to your neighbors, explaining what is wrong, organizing them and gathering volunteers willing to serve, then replace the Board either by recall or at the annual meeting.