I took a look & the Koso Instruction pdf section 5-12 page 19 seems to explain the ODO aspect
They use the terms Internal & External ODO, a round about way to explain anti tamper backup in ECU's so the backup is "Internal" & the Koso is "External", there are 2 lines of text in the instructions which are relevant
1/ User unable to adjust or clear internal ODO.
ie you cant change the backup value in ECU's
2/ When connecting to the meter for the first time, the total external mileage displays the ODO record value.
ie the Koso reads the ECU ODO value & sets "External" Koso ODO to the same value
You can only assume Koso has reverse engineered the CAN comms to have the ECU ODO values updated as per BMW dash
The ability to increase the "External" Koso ODO value will be as per the Dealer System ability to correct any mismatch in ODO values & only allowing an increase in value is appropriate to stop total ODO value tampering