OK, i want to run a theory by you guys regarding the FF's timeline: The Tigh we met at the beginning of the series is dead and has been replaced with a skin job created by Cavil in the original Tigh's image.
The timeline below uses X as the start of the series. FF_Tigh is the person known as Tigh that lived on earth 2000 yrs ago, Tigh is the person we meet in Season 1.
We know the following today:
X - 2000: FF_Tigh leaves Earth, heading to Colonies.
X - 40: FF arrive at Colonies and end First Cylon war by offering to create skinjobs for the Centurions. Tigh fought in this war with Adama.
X - 30: Cavil is created
X - 20: Cavil kills the FF including FF_Tigh and boxes them
X: Colonies are Nuked
X + 2: New Caprica. Tigh is captured and tortured.
Here's where my theory kicks in
X+2: Tigh is not just captured and tortured, but killed. FF_Tigh is resurrected in a body that looks like Tigh, with Tigh's memories overwriting FF_Tigh's own. [Cavil has mentioned that he can read memories directly from the brain and now FF_Tigh can know all the horror of the war that Tigh went through, therefore learning the lesson Cavil wanted to teach the FF].
X+2: The other FF were all on NC as well, therefore Cavil could have done the same thing with them at some point (Tory, Anders, Tyrol, Ellen)
Somehow I think that the head people have to do with the transfer of one person's memories into another's, two sets of memories, one brain. I don't know how this part fits in yet, but the FF timeline can now be reconciled.