Jeff,
While I can't say with evidence, it is my personal belief through my own experiences, that wholesale seed suppliers exist & point-of-sale seed companies are either contractually obligated to not disclose their sources, or prefer to limit potential competition by keeping their source to themselves. I've emailed a reputable small but growing seed company in the past & received a reply. I emailed them more recently asking about their testing of corn seed for potential GMO cross pollination & was ghosted.
Sure, many seed companies that
sell to the public via retail packets or
online sales grow their own seed, or contract with other small producers to grow it for them in keeping with their standards (I have heard of these stories from people who trial a new variety before it hits the seed catalogs). As these small businesses grow, so does their catalog, and in-turn, their need for more land/staff/growers/etc. Personally, I don't fault any of these companies for outsourcing some of their recurring bulk seed production. Where the problem lies, is at the Quality Control aspect. I'm sure that wherever these peppergate seeds were sourced from is getting an earful of complaints from every company they sell to. Chances are, that company will fold, get rebranded, and sell to the same seed sellers next year under a new promise of better oversight. That's just how these things work.
As for China, I'm not going down that road, but the supply chain for these commodities is no different than for any other with regard to wholesale goods.
Another story...Two years ago, I bought the same sweet corn variety from 4 different vendors that were sold in farm stores, big box hardware stores, & at every XXXmart around the country. 3 out of 4 ended up having worms hatch out of the kernels while in the packets, reducing the good seed to half or less. I wrote these companies, & included photos, & only one had the decency to reply & offer to send me some alternate seeds as replacement. Later, I went to those same stores that I bought them from, and all of the corn seed packets were riddled with moldy corn, frass, dead moths, etc. Sure looks like those seeds were all sourced from the same place to me...