It was not obvious to me that, when leveling up, unspent skill points would be saved for the next level. I figured it out only when I realized that you always got 6 skill points/level but at some point another level in a skill cost more than 6 skill points... which I think I realized at character level 4 or 5.
I've probably already screwed up any chance at getting one of the in-game NPCs or my PC up to top level in any skill, but I suppose I can create adventurers specifically to go pick the locks on leftover doors in late-game areas.