Here's how the PUP works.
A player must first be placed on the pre-season PUP before training camp, if he is determined unfit to practice in training camp. At the final cutdown, the pre-season PUP expires and the team must either trade, cut, activate to the 53-man roster, put on I.R., or add to the reserve-PUP list.
(Pass was placed on the reserve-PUP list on the final cutdown.)
If that happens, a player doesn't count against the 53-man roster limit and cannot practice until he is "activated off the PUP."
There is a 3 week window from the day after the week 6 game to the day after the week 9 game to "activate" the player off the PUP.
(Pass was activated the day after the Pats' week 9 game, or the Colts game.)
But then, he DOES NOT yet count against the 53-man roster. At that time, the player can begin practicing.
From there, the team has a 21-day window from the time of activation, while the player practices, to add the player to the 53-man roster, cut him, or IR him.
(The deadline for that 21-day window would have been either Monday or Tuesday of this coming week. But apparently because of the Faulk situation, the Patriots activated Pass today instead, adding him to the 53-man roster which was previously at 52.)