notoriety

Hopefully this is a simple question. I’m the Executor for an estate that includes property and investments, including ISAs. I’m slightly confused about the dates that I use for the valuations to calculate any CGT. It seems to be straightforward for property. The valuation of a house as accepted for IHT and for Probate would be subtracted from a future price on sale. For the ISA it seems that the base valuation will be that on the date that the investment is transferred to the beneficiary; since that’s when the ISA ends. I’m slightly less sure about the other investments. Do I use the value of them as reported to HMRC/Probate on the date of death or is it the value on the date that Probate was granted (or something else)?