After coming across a
thread with a similar issue, I decided to call Verizon. Without disclosing that I had a non-verizon device (I did say I bought it used and it didn't have the standard VZ apps), the rep confirmed that the ESN, MDN, and MSID matched what they had in their systems, so I'm good on that end.
It's been escalated to a "network repair team" and I'm expecting to hear back 24-48 hours.