The problem is not with TK (their ticket may indeed be T throughout) but with Thai: since this is a codeshare, TK's T may be mapping to a fare class that earns nothing with A3. This is basically what you have to find out. Just to show you how complicated (substitute with anything else you want) things may be, I recently flew a TATL (westwards LX, eastwards OS) with a ticket bought from LH, and I had the miles credited to M&B. LH's fare class (P) should have given me 0% throughout, but actually I got 200% from LX (both segments) and 100% from OS for the TATL segment and a flat 750 miles on the European one. Conclusion: Depending on your heart condition and your blood pressure, I would give up or try with Thai!