Pot marking Q

[simpson]

I found some nice Piher pots at a garage sale. They are marked "1M - 812M PIHER"

They seem to be linear taper as they read about .5m at the halfway position and about 1m at full position.

My question:
I know the "1M" refers to its rating of 1 megohm but what does the "812M" marking mean? Or, is that just some sort of stock number?