this is an odd one, a derelict salvaged tube with the fitting it came with, i would say its early 60's as the building it came from was 1964 and this was in a switch room and would have seen little use, however its rated at only 65 watts? not 65/80 or just 80 watts. Also it says RS on it, would this mean 'rapid start'? Sadly its a duff

Yeah that's an odd one and yes RS is rapid start? US market maybe?

its made in great Britain though, and was in a shopping centre in the midlands

Very odd trying to make our if that's a date code or a bit of rust on the tube

Looks like a smudged date code something 4 which makes it 1964