"The Rs and Us are actually a quite useless and meaningless things made by rockstar. I myself never understand the logic of needing something as dumb and useless like this but I tell you what they are exactly. It is no wonder why so many people don't know about this, even many ped creators have no idea at all nor to make a proper .ymt . That is why in many ped mods you download you are having 50 clothing slots with 50 texture slots each while the ped only has 2 or 3 models and a few textures in each if not just 1 .."
@Aurora11 Agreed. The most likely answer is 'R' never took modders into account when they built the core of the game. The mere fact all they've done with clothes for each DLC is rehash the same forms with slightly altered textures and that they still think their primary demo is '13-year-old boys' hence the sad amount of clothing and accessories available for MPF characters. That's good news about the heel fix you mentioned. On that line, I've had the weirdest deal with MP Clothes and textures for 'uppr's' and 'lowr's'.
Using MPC, I've input various uppr's and lowr's to create variable body types for MP characters (something 'R' never bothered with.) Strangely enough, textures for all the other character parts (hair, feet, etc.) the textures render just fine. But for some weird reason, only lowr's and uppr's generally don't render the textures. Now that said, 'nude' versions either won't render at all or render textures upon spawning or selection via a trainer (I generally use Menyoo.) But, when I select 'skin tones' from the 'mother or father' list and select a 'vanilla' type uppr, then go back to the one I wanted, it will render both the body part and the proper texture.
Clothing lowr's are pretty much broken in the mod as only about 4 lowr's from different modders load without issue. Anything else, even vanilla versions all have the 'flesh' texture or whatever texture from the previous loaded texture was. I've tried every suggestion from changing the texture name and others all which does not work. The one thing I've found is the game is trying to match the body part number with the texture number. What's weird is whatever the body part's orignial number is, that's what the broken ones try to match up. Stranger still, even when matching all numbers up (i.e. 'lowr_007_r.ydd' to 'lowr_diff_007_a_uni.ytd'), the lowr still goes 'meat' texture. I've discussed this with the mod creator at length and he can't figure it out. It's worse with the 'More Clothes' mod as it will only render the head, hair, 'p' accessories, 'jbib's' and 'feet.' None of the workarounds to get textures to work have any effect with that mod.
You seem to have a grip on how this stuff works. Perhaps you have an idea what's happening?