There were plenty of wow private server gold examples in vanilla of comparable skills piling up, and at times people exploited that. It is possible that the foundation way resistance and armor function is wrong on personal servers, which would also account for a lot of differences. However, my guess is that every armor reducing capability will stack with each other. In general in WoW Classic, comparable consequences piled, but the specific same ability didn't (which is the reason why only 1 battle shout could be busy, and why you can't just spam warriors to each of sunder armor and trash the boss).

This is. Just Blizzard had the original data. Personal servers use server code predicated on what was reverse engineered and since virtually all of the rewarding world data (spell mechnaics, loot tables, expertise prices, AI, pathing, dialog scripting, etc.) had to essentially be recreated from scratch. In many cases they did get things wrong because of incorrect knowledge or improper assumptions. In other cases things were intentionally altered like experience rates and rear porting new races out of newer DLC.One of all the things which I do gold in wow classic hope they do is give us appropriate widescreen support. This was fixed via a 3rd party patch and afterwards patched properly but 1.12.2 foundation has this matter.