The key word in s3A(5) is “assumed”.
Suppose I make a PET and, say, four years later I make a chargeable transfer. s3A(5) allows me to assume that the potential for the previous PET to become fully exempt will be realised when calculating any lifetime IHT on the chargeable transfer. To determine whether the potential for the PET to become fully exempt has or has not been realised, we need to look at s3A(4) - s3A(5) is not relevant for this purpose.
Applying s3A(4) to the specific query raised, we have to ask ourselves whether 15 January 2018 is seven years or more before 14 January 2025. I would submit that the date seven years before 14 January 2025 is 14 January 2018, in which case the test in s3A(4) results in the PET made on 15 January 2018 becoming a chargeable transfer.
Paul Thompson