The early limits on television picture quality

[ppppenguin]

I'm pretty sure it was standard by 1953. BECG's Project Vivat is using kit from that period and it's 1V of video and 75R co-ax throughout. https://becg.org.uk/projects/project-vivat/ I think that pulse distribution (sync, blanking line drive, field drive) are all at 2Vp-p which was standard on this side of The Pond. They used 4V in the USA. Marconi kit carried MB, LD, FD on a single EP8 connector. MS (and video) had its own co-ax with the then usual PL259/SO239 (UHF) connectors.

That narrows it to between 1936 and 1953.