Razors are tang-stamped before final heat treatment, not afterwards. If stamped afterwards the brittle metal has a tendency to break.
I have seen tang marks removed (or crudely obliterated) before, usually by means of a grinder, but this seems to have been the case mostly (only?) with razors from Germany during WW2 and sold in non-Axis countries.
Makers did occasionally buy in overstock and acquire the stock of defunct companies, as witness all the Le Grelot blanks, Klas Tornblom blanks and re-Wackered blanks that crop up from time to time. It's common enough in the knife world, too. I can see someone going to the trouble of grinding off another makers mark, but usually that is accompanied with a light etching of the current makers mark rather than re-stamping, which for reasons given above is not a good idea. The cheapness of the blanks would make it worthwhile if it was auctioned-off stock.
However, to buy-in fresh stock with someone else's mark and then go to the expense and labour of grinding said marks off seems like a big no-no, especially when they could have your own stamp applied at time of manufacture.
As well as that, there were special marks that were mainly a gum composition that could be removed by rubbing with a rag and spirit, as well as a very light etch which could easily be buffed off with hardly any effort available for makers who bought-in blades. Again, these were usually etched with the new makers mark.
Finally, there are a few complex interwoven design marks. It is hard to see from your photo, but it looks like "Sheffield Steel" is within the confines of a curving banner with other writing protruding top and bottom. Sprock razors have a 'slightly' similar mark, and I have seen a few others.
Attachment 124774
A larger, clearer, more sharply focused and well-lit shot of the tang after light cleaning might be helpful, as well as a shot of the blade ornament.
Regards,
Neil