Seems like it should be easy enough but some agents just want to do the bare minimum. Departing SAN on DL on an international itinerary with two different tickets on a variety of partner carriers was no sweat for an agent to check bags through to the final destination. Returning on KLM and connecting via Aeromexico with two different AM tickets was too much for the agent to digest. She wouldn't even look at the second ticket so we had to claim bags during the journey.

If it's not a true Delta partner, all bets are off. The same friendly SAN crew wouldn't check a bag through on a Hawaiian Airlines connecting flight booked on a separate ticket.
larity