Tried that, looked at a bunch of different airlines in the airline agreement, both domestic and international. There's no explanation for the codes, and even if there were, the codes are all the same whether it's for employee, employees' spouse or parents.

I googled the codes, but couldn't find any explanation or definitions at all.

Every airline on myidtravel listed my parents as ineligible, the only airline I can list them on is Spirit, off the team travel site. If that's the policy, so be it, but if not maybe HR knows what's up?