We have finally got to the issue of Quora. The rule is in Chapter 15and so applies to meetings. Rule 15.I.D.i says,
The quorum for business meetings of (this body) shall be 25 per cent of those members entitled to vote in attendance {or a fixed number to be agreed with the regional office of the Party}.
I understand that the NEC have agreed that for all member meetings, a quorum of 25 members can be agreed but delegated the decision as to whether the latter quorum can be used to the Regional Directors, some of whose decisions may seem capricious at times.
Here is the document, allegedly, no logo, no imprint, and no chain of custody, NEC Quorums guidance 17 January 2017
Quorum