Oh, I just use to screw around a lot with what I did know.
That was really only situational, I just used what I had to figure it out.
I honestly don't know what all those numbers mean specifically in the game, I just used Translhextion, my favorite Hex Editor, to compare two copies of Cave Story, one original and one touched by the npc.tbl editor.
All of the differences it found obviously had to be where the corruption was, and a few copy/paste tests showed that I was right. If I wanted to use the npc.tbl editor, I just had to make sure to copy that bunch of code over again to remove the corruption.
That was more simple logic than code knowledge.