The NWA pilots specifically have their call-back rights as part of the agreement between their management and ours for them to come to work here.
Pinnacle DOES make you resign your seniority; that said, there is a HUGE lack of follow-through from time to time on this. People have slipped through the cracks and some have gotten pestered (threatened) until they were forced to give the company their resignation letter to send to their previous employer.
Like everything else here, it's poorly administrated and you stand a 50/50 chance of not being made to resign.
All of this is information that's about a year old; things might have changed. They're so desperate at this point, they might not ask anything at all about seniority resignation.