It’s not the code that matters, it’s the data structure. Which is the same. Treasure classes haven’t changed. Even the old loot bugs aren’t fixed: 3 very simple loot generation bugs that can be fixed in 5 minutes
Modding is supported by blizzard (they even post some stuff related to modding in the patch notes). Hence you can unpack the data files and see them for yourself. To guide you through it, here’s the best possible article: https://diablo2.diablowiki.net/Item_Generation_Tutorial
I have studied this subject thoroughly, and the guide is correct. I have done some calculations here and there, and the drop calculator that comes the closes to the truth is the “german drop calculator”: http://mfb.bplaced.net/dropcalc/dropcalc.php?lang=en&patch=113&mode=lod&interface=default&window=false
The only things it gets wrong are:
- the countess rune drops (it’s really complex maths for the countess, where the same item can spawn on 2 branches of the treasure class graph)
- duriel (bug with TP scrolls, see details in the post I linked)
- snapchip shatter and frozenstein (bug with treasure class data, see details above)