Reference number scratch outs

[watchzealot]

Hi everyone. I've been collecting watches for years, but only recently gotten serious about buying my first Rolex. With that decision comes a lot of knowledge I need to gain about specific models and things to look out for.

I've been leaning towards an Oysterdate or Oyster Perpetual from the 1950's or 60's. In the course of my search, I've come across several watches that have the reference number scratched out and a new one added on the inside of the caseback. Is this legit? I've never seen it on a watch from another brand. I've attached a pic of one I found for your reference.

Sorry if this has been asked before, but I wasn't able to find anything using the search.