The supply chain has four roles: a synthesis lab makes the peptide; a filler puts it into vials, freeze-dries and labels them; a wholesaler sells those vials in bulk; and resellers or group-buy organizers sell them on. One company can play several roles. A reseller plays only the last. How Are Peptides Made? walks through the first two.
For purity, what matters is the batch, not the name on the website. If four shops sell the same batch, one lab result on that batch tells you about all four vials, storage and shipping aside, and a bad result does too. Check the batch number on your vial in the Peptide COA lookup.
The index records which shop submitted each test, the lab, the batch and the result. It doesn't record who synthesized or filled a vial, so it can't confirm a manufacturing claim either way. Each shop's own tests are on its page, reachable from peptide shops.
If you know a batch that's sold under several shop names, post the batch number and the shops' names (no links).