The rule on delegate entitlement in Chapter 3 says,

C3.I.1.B. Delegates duly appointed by CLPs to the number of one delegate for the first 749 individual members in the constituency or part thereof paying their membership dues as of 31 December in the previous year, and one further delegate for every additional 250 individual members in the constituency or part thereof. CLPs must also have paid any outstanding insurance premiums and other levies due before their delegation shall be accepted.  To increase the representation of women at Party conference, at least every second delegate from a CLP shall be a woman; where only one delegate is appointed this must be a woman at least in every other year. In a year where a CLP is required to send a female delegate, following a male delegate in the preceding year, but is unable to find one, they will not be entitled to send a man as delegate. In the following year, permission may be granted to send a male delegate if they demonstrate to the conference arrangements committee that they have made every effort to seek a woman delegate.

C3.I.1.C. Where the individual women’s membership in a constituency is 100 or more, an additional woman delegate may be appointed. Where the individual Young Labour membership in a constituency is 30 or more an additional delegate under the age of 27 may be appointed.

WTF does this mean?

I think,

If you have under 750 members, then you get 1 [ordinary/open place] delegate which must not be a man two years in a row. You may add two delegates using Rule ./C.

If you have over 750 members, then every second [ordinary/open place] delegate must be a woman. This means that for an odd sized delegation the delegation must be at least 50% female rounded down, but if the first delegate elected is female, then it’s at least 50% female rounded up. If you have an even number of delegates, then they must be at least 50% female.

It remains unclear what happens if you drop from 751 to less between conferences and had sent a man and a woman in open place positions to the conference prior.