I ran the following pgn extract command
pgn-extract --materialz "n3+q*r*b*p* n2+q*r*b*p*" --output knights.pgn db.pgn
I expected this to find games where at some point in the game, one side has three or more knights and the other side has two or more knights. However, the linked game was identified as one of the games that matched those criteria. At no point in this game does one side have three knights (or more) while the other has two (or more). One side has four while the other has one, but that's not what I expected. So, am I misunderstanding how the software works, or is there a bug in the software?
Edit: Another few examples of games it picked out: