I called AMEX to verify again just now (and to open a CS file). I called last night while at lounge and agent and their supervisor agreed i get in. I even noted the wording above to them. They took time to research and both said the actual policy has no exclusion about Sao Paulo. Just needs to be a Centurion Lounge per them. Posted here before I called in to open the CS complaint file.

Agent tonight again confirmed get access and that GRU is indeed an AMEX Centurion lounge. The lounge agents kept insisting it wasn't. Would've been weird as the lounge was dressed up as AMEX lounge, even had the wooden AMEX checkin desk.

I understand there's not many qualified flights for DL Reserve card out of GRU. (Only one DL operated and very few DL marketed codeshares from international terminal) However they were downright rude even with AMEX agents last night. Agent even told them swipe the card and it will show they get access. They wouldn't even do that.