Maybe something like an additional clause:
9.17.1 When governor positions become vacant outside of normal election terms, election procedures for their replacement are not required until the number of governors still in position falls below 9. Election procedures for any vacant governor positions may be started at any time by the NEC, but at their discretion may be deferred indefinitely until there are 4 or more vacant positions, after which election procedures should ordinarily begin as described in 9.17.
Or suitable rewording if it can be said or fitted in better, the intent is as follows:
Unlike the NEC where positions vacant do need to be filled and can't be left vacant for long, in the case of the board where there are 12 governors, if 1, 2, or perhaps even 3 governors stand down I believe the board can and should still be able to function entirely normally.
This is something I have suggested before (long ago) and having seen the recent vacancies and board elections I still believe this would be an improvement on what happened. We more or less managed, but section 9.17 put pressure on the NEC to begin internal party election procedures for just 2 governors at a time when it wasn't necessarily helpful, due to politics happening in the wider world outside PPUK. Then, additionally, we had a third resignation after a delay, again we more or less managed but it was a strain to make that work and comply with the existing constitutional requirements for election timescales, even though it was clearly sensible to hold a single combined election for all three vacancies if at all possible.
If election procedures were not required until at least 4 vacancies existed, then it would minimize the need for unnecessary internal politicking every time an odd 1 or 2 governors resign (which will doubtless happen periodically) and it would also ensure that most elections for the Board would be for several vacancies, also preferable since we use a Single Transferable Vote system for Board elections.
I suggest the NEC would still be able to start elections for any vacant positions at their discretion, since it might make operational sense to do so and they might wish to take the opportunity to inject new blood into an old Board, the intent of the proposal is that they would not be required to do so until there were sufficient vacancies to make it imperative.