[Question] ME fix edits vs others

[poppy]

I've been using Andrige's druid form pack for a while now, including his worgen cat, and also a bear -> furbolg MPQ from someone else I forget. I started trying to make my own model swaps by following some guides, but they all led to .exe errors. I looked around and saw that everyone says you have to use model edit fix to use custom edits now, but andrige's works without it.

My question is what makes Andrige's MPQs different from others? Why can't model swaps still be done without using model edit fix?