If IHT thresholds change while waiting for probate..

[Tiktokcringeydance]

Have NC for this.
My Ddad died just before christmas and his estate is being dealt with by solicitors. They applied for probate just before lockdown so anticipate it will take longer than they originally said, although they are still working as we have had some communication during lockdown.
I heard mooted that the gov could change (lower) IHT thresholds as part of measures to pay for the debt caused by cv19. As it stands we were told no IHT was due ...but if thresholds changed where his estate did go over that, would it be applied since probate has not yet been granted??

No, they never change the rates retrospectively. If changed, it will be changed for 'deaths after X date in the future'.

The probate registry and HMRC are both slow at the moment, not helped by a recent change in forms , and a new 'efficient' online system...

Thank you. I wasnt sure.
We are coming to the end of a fixed mortgage rate and anticipate paying it off once Ddads house is sold. It would make a difference to what deal we go for if I thought there might be IHT to pay.