Yes, those two fields are high byte extensions of the backup counter and backup sequence fields in the master block. The backup counter was extended to three bytes in 12.0 for all Type II storage areas using a spare byte in the headers. The master block doesn't have this spare byte in the header, so a separate, spare byte was selected. The backup sequence is the last successful backup counter value, so it also needs to hold up to three bytes. The values are pieced together whenever they are retrieved and set at runtime.

Dbrpr should display them as 1 byte, I'll file a bug to fix that.