There were five Battlestars at the Peace Conference. That's what the script called for. Never anywhere has any official source, document or script stated that there there were twelve Battlestars, one for each colony. The earliest mention I can find of that inaccuracy is an inadequate fan produced booklet called "The Colonial Warrior's Technical Manual", published in 1988 by Space Waste. There are so many gross inaccuracies in there that it wouldn't be feasible to respond to the publication. Besides, are you going to put faith into a document published by "Space Waste"?
A second draft of the pilot script that I have specifically mentions "Five flying Battlestars", putting to rest the fan theory of, "There were twelve, but we only saw five because they didn't have enough money."
A direct quote from Glen Larson (series creator) at the 1993 Galactica 15 Yahren Reunion convention, in response to a question regarding the twelve Battlestar names, "We never arrived that there were twelve Battlestars. We only actually shot the Atlantia, the Pegasus, the Galactica. I can't think of any others."
In total, there are only seven Battlestars I would consider canon. Debate is welcome.
These five were at the Peace Conference:
Sources of the Battlestar names:
Shown on screen during the course of the series
That's it. To debunk the others:
Ship mentioned in background dialog of premier