Hi!
It doesn't work that way.
Some airlines have lists, while others don't. In some airlines, if you're not on the official list, you can't jumpseat. On others they'll let you JS even if you're not on the list. Others have NO lists, so anyone, basically, can jumpseat. Others may have a list, but ALSO let ANY -121 carrier jumpseat, so then USA Jet pilots can JS.
Other airlines use CASS instead of a list, so all CASS people can jumpseat.
HOWEVER, USA Jet has a 3-letter identifier (this is a new development from the FAA), and all the "old" airlines only had a 2-letter ID. So, some airlines, where we are in CASS and/or on the list, have software that will ONLY accept a 2-letter ID. If you get one of these, you can still JS, but only in the back, as the old 2-letter software isn't compatible with the "JUS" code, so they can't legally let you in the cockpit.
It's ALWAYS up to the captain, so they may not let you on, or they may let you on, regardless of the situation.
cliff
YIP