Windshield numbers?

[SFcarbuff]

I was preparing my original winshield to reinstall and notice the numbers 15-12 in the passenger side lower corner.   My son also is re-doing his original winshield in his c code fastback.  He also has similar numbers.  Both cars are end of March , San Jose built cars.   Just curious if anyone knows the meaning of these numbers?  Thanks

[CharlesTurner]

Seen the same on SJ cars and also other assembly plant cars.  Probably a rotation number or something to ID that a particular type of windshield went in a car optioned for that specific type.

[SFcarbuff]

Thanks, Makes since, my car has a plain window and the c code has tint.  Different numbers.