1) So, if my character is Squire at 0-level, he is trained in a longsword. He then keeps that proficiency when he becomes level-1, even if he became a class that didn't have longsword as a trained weapon. Right?
2) During the first adventure, he picks up a battleaxe from a dead foe and uses it. Is he untrained in it? (The rules say the untrained penalty is waived for all 0-level characters. But they also say that he is considered trained in the last weapon he fought with. When he first picks up the axe, is he trained in it, since he hasn't yet fought with it?) When he hits 1st-level, is he now trained in both longsword and battleaxe?
3) During the adventure, this same dude fights with a mace, a staff, darts, and finally a lance. He hits first level. He is now proficient in longsword and lance, but not the other weapons?
How I would rule these:
1. Yes. So wizard with long sword? Fine.
2. No. He is not trained in battleaxe, the penalty was just waived for 0-lvl play. He is still proficient with long sword.
3. No, just the last weapon he fought with.
In actual play, I just said they could have a proficiency with any one weapon they fought with during 0-level play.