Can a DOV vary a IIP?

If A died leaving an IIP to B in Will (not married). B died 18 months later remaining in property (owned 50/50). Before the 2nd anniversary of A death, A’s executors execute DOV with substituted Will leaving share of property directly to children.

I had thought that the beneficial IIP could not be varied under s142(4) IHTA 1984?

Trying to consider the IHT position of B and whether the IHT account of B simply only reports their half share of the property and disregards the IIP which was in the original Will effective when B died