First of all, Assurion does not provide you with a "new" phone. They provide your with a refurbished phone. They don't go out and purchase "new" phones to replace your stolen phone. The "backorder" in the supply chain is Assurion waiting for a refurbished unit to send you.
So, they are waiting for a new supply of "refurbished" phones. Why don't they ask the police detectives I spoke with which of the gas stations that my phone thief could have pawned off MY phone only to resell it. I'm pretty sure the phone trafficking is how many "refurbished" phones get back on to the market.
Actually, it is more likely broken phones returned for insurance reason which are then refurbished. Not everyone who files an insurance claim is the result of a stolen phone. These refurbished phones could also be phones exchanged at Verizon for whatever reason for a different model which are then sold to Assurion, refurbished and used as insurance replacements.
When you report your phone as stolen to Verizon, the phone ID is blacklisted so that it cannot be used on any provider. Using these as an insurance replacement would not help you much.