Why does a XBEE firmare change also change the Serial Number SH/SL?

I changed the firmware on my XBP9B-XCST-002 (Rev. R) XBEE modules from:

Product Family: XBP9B-XC
Function Set: XBEE-PRO XSC (S3B) 19200
Firmware Version: 3114 (Newest)


Product Family: XBP9B-DP
Function Set: XBEE-PRO 900HP 10K
Firmware Version: 1075 (Newest)

It works fine, but I noticed parameter SH and SL (higher and lower part of the serial number) changed too. Is this normal that a firmware change also changes the serial number? Now the serial number does not correspond to the label-printed MAC number anymore.

You change from a 16 bit serial number that was supported by the XSC product to a 64 bit number that is supported by the XBee PRO 900 HP product and its protocols.