CG37733 | Absolute entitlement: class closing rules: possible birth of children
From HM Revenue & Customs · Capital Gains Manual
In cases of this kind there are three possible dates on which absolute entitlement could be said to have occurred.
The date upon which the incapacity arose
the date upon which the trustees became aware of the situation, or
the date upon which they decided to act on the basis of their knowledge.
In the Board’s view the last of these is correct.