From the examples I've seen, I think you may be spot on. Auto Computer Exchange out of Florida seems to have cornered the market on used ECM's, but they have an absolutely horrible track record... an F with the BBB.
The last time I checked a couple of years ago, you could still order a refurbished ECM though Cummins, but you had to pay dearly for it... like a couple of thousand dollars if I remember correctly. But it's probably safe to assume it'd truly be refurbished if Cummins sells it and puts their name behind it.
John L.