Vintage BMW Motorcycle Owners

Does anyone out there know what the number cast into the top of the timing case on R52, R62 and possible R11 S1 mean?
Most seem to have a smooth case, but some look to have a 3 or a 4 cast into it.

Thanks for any information.

Lee

My R52 has a 4 on it, and I think Erik Bahl's R63 also has a 4. I don't know the origin, but I would guess it identifies the company that did the castings, or maybe if BMW did the casting, then it's the casting mold number. Just a guess.