I understand what you're saying, but on many cars ( I thought it was most ) the EEPROM in the cluster always held onto the genuine millage or logged any change, even though the ODO displayed the adjusted millage. This was some Euro directive to stop clocking. I remember Watchdog investigating clocked cars by checking the genuine millage still held on the cluster EEPROM.
Clocking was more then likely planned, so having it serviced would have given the game away ( les then a year old and with a planned clock of less then 10k, no history would be recorded)
Trading Standards said it would be a difficult one to prove for an individual seller, but the owner has passed on the details.