The facts are that they were all the same except for a couple changes and they were painted many colors and used on several series of cars. What's your explanation for the numbers stamped on the tops?
Robert what "facts are"?
The FACT is that hardtops if not ordered with a car specially or on a GT which were colour matched to the body were all painted black by Rootes.. this system succeeds the series 3 cars .. all Series I/II were black unless specially ordered otherwise.... that's the FACT.
Your assertion they were sent from Rootes "as black or white" generically is wrong.
As for my explanation of the parts numbers, I don't have one, it could be to do with the changes in the drain rail channels..could be to do with the series of production.. they would not have been vin specific.
You often ask "what if's?" And question if the archive would know .... Maybe you should do some leg work on that