To be honest, if somebody had mentioned BS317 with no particular context, I wouldn't have even recognized the number as an electrical standard.
I've just checked back in the oldest A.S.E.E. guide I have, but as that relates to the 13th edition of I.E.E. Regs. (1955), it has no mention of BS317 at all.
The standard 2/5/15-amp connectors in BS546 were all in use prior to 1950, so I would assume that all were also in BS317, but as for what might have been in BS317 but not BS546 I can only take an educated guess.
One candidate might be the 2-pin (non-grounding) version of the 15A plug and socket. These were quite common in pre-war properties, but were dropped in later years. I'm not sure the exact date they ceased to be made, but it could have been as late as 1950.
Similarly, the BS1363 standard has been updated in more recent years, not to change the overall plug configuration but to add things like the sleeved line/neutral pins (the plug shown on that 1947 page is a relatively new one).
I can't work out the seven connectors referred to there. If the 3-pin 15A was still specified, what was the odd extra one? If 3-pin 15A had already been dropped, then we're two short.
I actually have an multi-adaptor which includes a strange British plug. Ungrounded, two pin, small. I think I've seen this type of plug called a BS 3?? plug, where I have forgotten the two last digits... I do remember a Google search for this standard turned up blank. Could very well be BS 317.