South Carolina will accept another state's resale certificate number. On its own form, on purpose.
I build certificate validation software, which means I read a lot of state tax rules. This one is curious because it feels contrary to the entire point of the process. A resale certificate exists so a state can trace who's not paying sales tax and why. South Carolina looked at that and said: a Georgia number is fine. A Texas number is fine. Write it on our ST-8A and you're good.
Six hundred miles west, Louisiana accepts nothing but its own state-issued certificate. Not other states' forms. Not the multi-state MTC form that works in thirty-plus states. Nothing.
Same country. Same month. Same document, in theory.
That's the real lesson for anyone selling wholesale into multiple states: acceptance rules aren't on a spectrum you can intuit. They're fifty independent decisions, and the strict states and the permissive ones look identical from the outside. The certificate your buyer sends you isn't valid because it's filled out correctly. It's valid because the specific state that governs your specific sale decided to accept that specific document.
You either look it up every time, or you build a system that already knows.
That's the one we built: our free validator reads a certificate, applies the rules for the state that governs the sale, and cites the rule behind anything that fails -- in about fifteen seconds. Checking numbers against state-published registry data (TX & PA today) is part of our plans.
(General education, not tax advice -- your state DOR or a SALT professional is the authority for your situation.)