We are always glad to help. It was good of Plonker, that he got you mostly sorted.
The thing about why some girls have .rgirlsx files and others do not, is simple. You can always have one and only one girl generated in-game from a .girlsx file, but you can get potentially an infinite number of (randomly named) girls from an .rgirlsx file. Packs that have only a few images in the critical picture categories can get kind of boring if you have 20 copies of her in your game. In general, porn girls have tons of pictures, so I generally make both unique and random files for them. (Yes, there are exceptions. *shrug*) Celebrities depend more upon how popular the woman is in the faker community, and I generally find it difficult to fill out all the sex categories with enough variety, so I generally do NOT include .rgirlsx files for celebrities.
If you are looking to make packs, you need to get into the "Docs&Tools" subdirectory where the game is installed.
Start playing with making the files using the Character and Item tool, called WMEdit. You can load up the existing .girlsx and .rgirlsx files and examine how they are constructed. I recommend that as a first step towards learning how to make your own packs.