PLR MRR RR sites - who is their source?

Been looking into joining a PLR/MRR/RR member site.

Observation 1: There are 3 that are the most popular PLRassassin, IDplr and resale-rights-weekly.

Observation 2: all 3 sites have exactly the same products.

Observation 3: a lot of the better products are personal use only - meaning you don't have the rights to ("legally") resell them, give them away, rewrite them, etc. as a member of the PLR site.

QUESTION: these sites are obviously getting the resale rights or giveaway rights somewhere. Anyone know who their source is?

I'm willing to signup under your affiliate link if I can verify the source.

PS: Sorry if this isn't the best section to post this in.

I'm also looking for thi information and I have been finding information about that for a long time but couldn't find. I hope someone can help me here.