It's not unprecidented though, MKM uses Panasonic's MID for DVD-RAM for instance.

Also, I highly doubt it will continue like this. By the time it reaches North America it very well may be a proper MKM code.

Getting details on serials for both types of discs (Mitsubishi brand and That's brand) would be good though, and I'll try to pick the brain of one of my other sources who might be able to shed a little more light on things.