A year ago I needed a lounge at JNB International as at the time I had slipped to STARSilver and could not use the contract lounge associated to LH flights. I did have a PRIORITY PASS membership through my Canadian Diners|Mastercard, so used the PREMIER lounge. (This is why PP is not a CENTURIAN benefit for NAmerican cardholders.) Beside the door to the Premier Lounge, I noticed an AMEX logo as well as the DINERS logo. However, there was a similar note under the AMEX logo advising only South African-issued cards would be honoured for entry. (I was able to forego the PP charge by showing my DINERS card, which was accepted as an affiliate for free entry. Seems DINERS has no such national restriction.)

Each AMEX country has a specific set of lounges associated with free entry. The US and Canadian Platinum program are similar in providing airport lounge access to CO, DL and NW lounges but not to lounges of other airlines which might be accessible to AMEX Plat cards issued in other countries. This is complex and confusing, but "goes with the territory".

And to confuse matters further, AMEX does have its own branded lounges at many airports in Latin America.