RNRB and pre RNRB Discretionary Trust

I have a situation where Husband died in 2014 created a NRBDT. The assets comprised in the estate were a 50% interest in the matrimonial home and some cash. All assets were transferred to Wife and the trustees hold an Equitable Charge of the NRB (linked to inflation). The Trustees have a restriction on the Land Registry records in their favour to “protect their position”.

In terms of Wife’s estate for IHT, do forum members agree that her PR’s can deduct form her chargeable estate the Charge along with her own NRB and both her own RNRB and the transferrable RNRB from her late husband?

My rationale is that that RNRB was not in force at the time of husband’s death and could not have been used. The following exchange seems to support this view - Transferable Residence Nil Rate Band Query

I think what is causing some concern is the Trustees having an entry on the Land registry and this in some way restricting the TNRB claim but am not sure that really matters.

Thoughts appreciated, thanks