I suggest that PCB number is in firmware in crypted (so as ID-PID-SID for map ID in HEX) Garmin format like other similar numbers...
For example, HEX expresion for voice files present in body of that files - device find and show PartNumber in inventory,
<PartNumber>006-D0397-00</PartNumber> <FileName>English_American_.vpm</FileName>
<PartNumber>006-D0400-00</PartNumber> <FileName>Deutsch__.vpm</FileName>
<PartNumber>006-D0401-00</PartNumber> <FileName>Francais_European_.vpm</FileName>