Thanks, Blake.
Of the 3 VPP Codes that I had, only one is assigned to an actual device. The other two say they have been redeemed by "unknown device" (this is likely due to our attempts at removing them - we took the devices out of Meraki). For the one device that is known, I added it to the scope, verified the app showed in Meraki SDB, then removed it from the scope. The device no longer shows that app in Meraki SDB, but the VPP Code has not been released.
It is odd, because the app never installed on the device - it failed. I'm not sure what I'll be able to do on the other devices that are listed as "unknown".
I ended up purchasing another code and applying it to another iPad. It installed, but Meraki is reporting its status as "Not installed". The VPP code is redeemed.
Strange.