Fare class availability data essential comes from the same place for everyone (except for the UA itself of course -- it supplies the info).

But not sure what the linkage to Irrops is?
In Irrops you do not need the same fare class as you were ticket ted. It makes the rebooking process a bit easier but it is not a barrier in irrops.

All you need are seats available in your booked cabin.
Seat availability can change very quickly in irrops and from the time you check until the time you are being changed it is not uncommon for seats to disappear.

FlightStats will not have award / upgrade availability.