True, but the error wasn't flagging and there was no visual distortion like there was after installing the new WW. When I rolled back and everything worked fine from no exceptions to no visual distortion, it isolated the issue to the updated WW.
Because it isn't the kind of error that causes crashes or last exceptions, it won't appear on logs. It's like having two default replacement skins for example, the game will detect and load both but will only use the one that loads first. This loading priority is determined by where the files are placed withing the mods folder and their names.
If the other rig that you have is loading after ww or it is exactly the same rig, it won't cause noticeable issues other than wasting resources. But if it has different bones and it is loading before ww, some body parts will look distorted during animations because they weren't made for that rig.
The new ww rig has added some new bones and removed others. That will cause the dreaded visual distortions with sims that have body parts that use some of those removed bones (tongues, long penises, etc). And in the future when people start making their new animations with this new rig, they won't work for those that are still using different rigs and outdated body parts.
Either way, as I said earlier: just because you don't see any visual distortion or error notification with the old version it doesn't mean that there isn't a conflict. You'll need to find that other rig eventually, unless you're planning to not update ww and your game anymore, you won't download new animations and you're fine with having something there that isn't being used