Are worn out serial numbers a problem?

[b12]

I've been looking at vintage models from the 50s lately and a couple of them have serial numbers that are barely visible -- you almost need a magnifying class to see the remnants.

What are people's views on buying such a watch? If the serial number becomes invisible, does the watch lose value? Is there somewhere else on these watches (reference 6422, 6694, etc.) that you'd find the serial numbers? Interested in thoughts from this group. Many thanks.