If you have a real ID50 (and I mean not a Standby ID50) you are not off loadable. Or to be precise, you are as much off loadable as any other full fare paying guest showing up "late" on an overbooked flight...
Negative an ID XX (anything) is
not a full fare ticket, it is a sub-load ticket.
I have, on occasion, shown up at the gate with a full fare ticket, and watched ID50's being offloaded, to accomodate full fare passengers.
Happens all the time.
You need to know the rules.
