Aldous wrote: In other words, when you go beyond the 7 year period up to 14 years, what actually counts to use up the nrb?
A PET within 7 years before a CLT that was within 7 years of death utilises the NRB available to the CLT and hence in turn to the death estate.
More generally, your objective of trying to understand whether you, as an individual, may have a liability to IHT as result of the death of your grandparent(s) is understandable. You’ve done well to read IHTA 1984 and to seek to understand it. There is intellectual satisfaction to be had from acquiring the knowledge to be able to argue your position.
However your individual situation is just one piece in the” jigsaw” of your gparent’s specific financial circumstances – value and composition of death estates; terms of their wills; structure, purpose and value of lifetime gifts including yours etc - and it is that total “jigsaw” that will decide if there is any liability to IHT on anyone’s account, nevermind yours.
Unless and until you can give detailed information about those other pieces comprising the aggregated jigsaw and the reasons given, if any, by the personal representative(s)/HMRC as to why they believe you have any liability to IHT, I doubt it is possible to add more helpful comments than have been previously posted by Maths and, to a much lesser extent, myself.