Originally Posted by prathetkrungthep

The wording that appears in TIMATIC is "passengers who have transited or been in ..." so yes in that sense the non-Schengen part of the terminal still counts. Now the question is whether this will be enforced or if this could be enforced at all during your travel back. Since you will just transit the non-Schengen part, there is no obvious way for anyone to tell on your return that you have been through FRA (since obviously your passport would not be stamped at the German border.) But then of course TK could probably see your outbound segments on the reservation when you check-in at ASR or transit in IST.

If you were to travel back to the US via FRA then you would be denied boarding since LH enforces this by only boarding US citizens, permanent residents, and non-residents with exempted visa types. What I suspect will most likely happen for you, is you will be asked on check-in at ASR (and maybe before boarding at IST) if you have been in the Schengen Area (or UK, Ireland, China, Iran, India, or Brazil) in the past 14 days and they will take your word with whatever you answer. Personally I would not run the risk though and just try to explain the situation to an LH call-center agent and see if they can accommodate you on a different routing, change the ticket for a later date, or do a travel voucher.