Most (if not all) of them were renamed when they went to Mesaba. For example:
N321PX = N31XJ
http://www.airfleets.net/ficheapp/plane-sf3-31.htm
Mesaba took over direct operation of aircraft that were being operated by Express I. It was a near seamless transfer of assets. Only difference was that the former pilots had to surrender half to two thirds of their longevity to keep operating them.
I did not realize this about the A models either, the N number change lead to the confusion. I started pulling up A model N numbers and found a few that were transferred, but about an equal number that don't show a previous ownership. Do you know exactly how many were transferred? Or who owned the aircraft or leases? NWA or 9E? I know all the B+'s came from the factory to XJ.
Doesn't really change any of my previous thoughts on the LOA. The pilots were
awarded a job and longevity to come to XJ. At a loss of seniority to some XJs at the time. Had they stayed at 9E they would've been furloughed. Did you offer Freedom a deal like this when you took their airplanes? I would have been happy to take the 2-1 deal in 2002, instead of downgrading. I bet some FOs at the time would have taken the deal instead of being furloughed at the time too.