Nil rate band

Could someone tell me which gifts are deductible from the Nil rate band and from which period?

There is an exercise of which solution confuses me.
30/09/2003 CLT1 of £200,000 was made to a trust
30/09/2007 CLT2 of £300,000 was made to the same trust
31/08/2014 The donor has died

Q: Calculate the lifetime IHT payable on the gift on 30/09/2007 and any additional IHT payable following the donor’s death. Nil rate band in 2007/08 was £300,000.

A:lifetime IHT payable 48,500 coming from £300k-AE 2007/08 (£3k)-AE 2006/07(£3k)-remaining NRB (£100k) multiplied by 0.25 as the donor paid the IHT.
This also gives the gross figure of the gift which is £342.5k. So far so good..

But then, when the donor dies, the solution advise to deduct £200k from £325k to get the remaining NRB. Why?