I suppose as a summary answer to the original question one could say that in the late 1940s, Mullard offered both the EF42/UF42 and the EF91 for TV and other applications requiring high-slope pentodes, whereas Philips generally offered only the EF42/UF42. The Mullard duality probably stemmed from the UK competitive situation, wherein several majors were offering complete B7G receiving ranges.
Philips developed the EF80 as an improved/optimized successor to the EF42/UF42, with a fairly quick turnover from one to the other. Likewise Mullard also adopted the EF80 from its initial availability, quickly replacing the EF42/UF42. The EF91 remained in the range for industrial and miscellaneous purposes, so was still available for TV and radio applications. But for TV (and some radio) applications, the EF80 was the better choice, so there was a turnover from the EF91 to this valve, although at a slower pace than was the case with the turnover from the EF42/UF42.
The Mullard late 1940s duality was also apparent in its simultaneous offering of the EB41 and EB91 for receiving applications, as recorded in the concurrent thread Why Both EAA91 and EB91? (
https://www.vintage-radio.net/forum/...d.php?t=160476).
Cheers,