Why does its level even count as capped if the Growth Limit shows 66? How did it occasionally digivolve from 60 to 61, if its level was displaying in color red and I didn't raise its aptitude? But the Digimon is at level 61 now and can't get any EXP in battles, despite actually not hitting the level cap mentioned in its stats. At this point I finally paid attention to Piedmon's stats and saw that its Growth Limit is actually lvl 66. And after every single battle a "Level Up" screen pops up which shows a level up from level 61. Now its level is 61, and is capped (displayed as red) again.
I didn't Digivolve/Degenerate it to raise its Aptitude, so I've no idea how that happened. I didn't even look at its stats, until after 20 or so battles it suddenly leveled up despite the "level cap". It was a level 60 Piedmon, and its level was already capped at the moment I got it (displayed in red in battle results, and couldn't get any more EXP). There's a strange thing happening to one of the Digimon I got in the trade. I know you're not really supposed to have powerful Digimon right from the start, and they will often disobey in battle, just like in Pokemon games, but it works for me, and it's beside the point of this post and my question anyway. Long story short, having never played the first Digimon World DS, I decided to breeze through it before moving to the next games, so I got my friend who finished the game a long time ago to trade me a few really powerful Digimon from their playthrough to help me.