Actually all the 550s that were at the Motorola factory and in the Voom warehouse were changed over to 505s.
The 550s that were shipped to dealers and then sent back to Voom were shipped back to Motorola. They may or may have not been authorized to Voom service and been in service. These are the units that are reflashed with SC firmware, have the SC faceplace installed and ATSC tuner removed. These are the 505a units.