Was in trouble with Copa interlining my bag on separate tickets. Got a business class ticket with Copa BOG-PTY-FLL and separate ticket with United FLL-IAD with a very short connecting time in FLL (no chances to recheck the bag, just a time to pass the Immigration and to run to my gate).
United told me - just show your second ticket and your bag will be checked until the final destination, we got an interline agreement.
Thanks God - was very early on a check-in in Bogota. They vigorously denied to check the bag to IAD and told it is a policy if they don't see my next flights in their system and tickets are separate. We argued for more than an hour! Spoken with the check-in supervisor, called United 1K, and they talked to Copa... As a result, they did me a favor and called their high-ranked manager in the city office and made an exception. But I was very close to loose my flight from FLL (the last one on that day) because of the situation.
Had the same issue with Copa contract staff at GYE. They didn’t know how to tag all the way thru. It was 2am so I didn’t fight and had time at PUJ to recheck bags. Pretty pathetic that a Star Alliance partner doesn’t know how to do this.