Combining Age groups - when to stop combining?

[rdunlop]

Section 1.3.2 says

The convention host must combine age groups with less than six riders (three riders for
smaller conventions) if needed. This means that published age groups are not guaranteed.
This can be done on a per-event (= per-discipline) basis.

I think that there should be a cut-off date for this.
If one-week in advance of the competition, we have a certain number of riders...do we combine age groups at that point? What if people drop out the day of competition? what if only 3 riders show up to race? Do we combine after that point?

This rule should be clearer to provide more guidance about this.