The M4D reefer is the PC&F reefer the NRDX ColdTrain reefers were rebuilt from... also good for PC&F R-70-19 through R-70-25 classes (the funky roof... earlier classes were similar, just with a peaked roof)...
I haven't really tried to compile a roster... here's what I do have:
PFE/UPFE/UPRX/SPFE obviously the largest owner... PFE bought 3000, UPFE and SPFE each bought 600 after the PFE split.
The original ARMN had a few (maybe 25), but since all their classes got lumped into a single UPFE number series, with no order.. I don't know how many
The reincarnated ARMN, i.e, UP, has a boatload of rebuilt former UPFE cars.
SPFE sold at least 450 cars to FGE, these had the FGMR mars on them... they also sold some 180 to REMX, and 140 to San Luis Central (SLC)
Right before the UP/SP merger, they sold another 400 to Greenbrier, these became the Golden West Srvice (VCY) cars... 200 of these came back to UPFE
NPM/WFCX/BNFE had 700... 400 bought new by BNFE, 50 coming from NP, and the rest from GN.
Sante Fe had 400 as well (SFRC)... BNSF sold 15 of them to SLC... these may be the BNSF marked cars today.
Milwaukee Road had 200... 60 sold to SLC.
BAR had 100.. all to Wisconsin & Southern, who sold 50 to Green Bay & Western
Soo Line had a whopping 10...
Great Lakes Central, under Tuscola & Saginaw Bay has at least 10... somebody's former cars (UPFE?)
Wisconsin Central has/had some... 11xxx series... unknown how many or where from.