Hi. I have submitted an issue on the forge version (https://github.com/seymourimadeit/guardvillagers/issues/203) providing a few feedback when working on ressource packs with Guard villagers.
Any other feedback is obviously welcome :)

Some update about that (you might know already...)
The textures now are in
assets\guardvillagers\textures\entity\guard
There are two files: guard_steve and guard plus a folder guard_variants for biome variation with these files:

looking forward for these change in Fabric too. It's gonna make ressource pack update really more easy, and less texture means less disk space/reload time faster :D