Yes, it displays the stats on all of your observed hands for a particular player. So if you played with a guy a month ago, you will see those old stats on him if you happen to sit with him again. I've sat with plenty of people I don't remember ever playing, yet have hands on.
As for watching other tables...
That is data mining and is not allowed on websites. However, I believe that PokerTracker 3 will watch and record up to 30 hands at other tables on PokerStars
. After 30 hands you have to wait 30 minutes and restart PokerTracker before it will import another 30.