I may be wrong, but I believe the production number was just to keep track of the car (and it's parts) during production. I don't think there would be any pattern to them, or any differences for LHD/RHD cars.
I don't think I've ever seen how many RHD cars were made, but I'm sure this info is kept some place.
Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both tops
1994 E420