In reply to:

It appears to be stored in bytes 0x51 - 0x53 of the flash savearea.

Would somebody update the relevant part of RioCar.Org with this, please? The interpretation can be found elsewhere in this thread; in brief, it's a series of directory indices.
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Toby Speight
030103016 (80GB Mk2a, blue)
030102806 (0GB Mk2a, blue)