Can Sprint phones be rendered unable to activate due to an MDN issue?

[JedC]

Quick little background: I work for a third party cell phone resale service. We have a rigorous testing process in place, which includes testing all normal functionality of phones, and making sure the ESN is clear. We've had a couple issues with Sprint phones recently, so I figured I'd post here to see if I can get help in figuring this out.

The first issue was with a bunch of Samsung Instinct 2s that we sold. Older phones, sure, but all checked out fine, ESNs were good. The customer (who was another reseller himself) said that Sprint would not activate the phones. Even though they had good Sprint ESNs which they even acknowledged, they were "not in the Sprint database" and he said it could be because the MDNs were wiped.

More recently, we had a customer with an Evo 3D who encountered a similar issue. ESN was valid and clear, but the rep at the Sprint store couldn't get the phone activated no matter what he tried.

So, what's the deal here? Is it possible that this is an issue with phones being flashed too many times? Would this happen if a phone is flashed from Sprint to some random other carrier and then flashed back? Or is it something else entirely? Any help on this matter would be greatly appreciated so that I can inform my testing team on what to watch out for.