Just to report back on this, I flew yesterday. Was only able to check in online for the Copa flight. Check in with Copa in BOG , they accepted my checked luggage without any issues and at no charge (which should have been the case, as I was in business and it was within the baggage allowance). Issued BP's for both Copa and TK flights. Upon arrival at PTY, had to go to a special transfer desk that had been set up for the TK flights (there were 2 on this day), and there I received a TK boarding pass before departure. No issues of any kind (except boarding the TK flight, which is always a circus) along the entire trip