I remember starting on a domestic AC to International QR and then transferring in DOH QR to QR. It was a separate ticket on AC and separate on QR. The first check in agent was a veteran who asked me if I wanted my bags thru checked to the final destination. I asked her if this was possible as knowing they were separate tickets and not the same alliance either. She said she would do it and added my bags but she did explain to me that I needed to go the transfers in DOH and get my onward boarding card. I was happy that I did not have to get out in DOH and collect my bags and check them in again. I think some agents do not seem to understand that they can tag the baggage for onward without issuing the boarding pass for that final sector.