In article , philrichards1
@blueyonder.co.uk says...

First question: Roughly when did Lower Regent Street get renamed into
Regent Street?

Second Question: Is it simply worth firing off a complaint to LUL to ask
why the street exit signs haven't been changed? I'm guessing they
haven't been changed is they fit in with the décor of the station and
would be too expensive or impossible to replace or correct.

Was it ever officially Lower Regent Street?

I have various Kelly's Post Office Directories and London atlases of
different ages and all seem to show just Regent Street [SW1 south of
Piccadilly Circus].

Maybe Mr Jelf knows.