Couple of data points for everyone. Got bounced twice in Frankfurt. Both were clearly stated in the Amex access rules so was just checking to see how strict they were.
Had a connecting LH flight in Y after arriving on SQ. Flying to Italy so was in Schengen area T1A. Was told only had access at Non-Schengen T1B lounges.
Early morning departure on SQ back to US and tried at T1B Non-Schengen and was denied based on not flying LH Group. Had taken LH in the night before and didn't occur to me to try access with the arrival boarding pass though I suspect since not same day, still would have been bounced.
They were very nice about it and said there had been a lot of confusion from customers. I tried using the *A angle but was told strictly limited to LH group. They seemed well aware of the program and obviously knew the access rules.
Potentially great benefit though a little limited in scope. Not sure how many Swiss/ Austrian flights out of FRA are non-Schengen. So really they're just saying LH with most of those non-Schengen being long haul out of Europe. A Plat card holder in long haul coach on LH without status now gets access to Biz lounge. But anyone with *G already had access to the Senator Lounge.
The Cent first class benefit is obviously great b/c that lounge's access is tightly restricted.