Amortisation is not allowable for tax purposes. It is purely an accounting issue, it is reversed back out of your income statement when you calculate taxable profits. It is also an expense, rather than revenue; you're writing down the value of an asset and lowering the overall value of the club.
It's worth noting that the club's accounting date is 30 June - meaning that the departures of Kamara and Greening fall into the period. The period would also include the first quarter of Bryan's fee, as well as quite possibly the last quarter of AJ's and assorted other transfer fees. It's also worth noting that depreciation/amortisation is not just player fees - all assets acquired and held by the club will be depreciated, with the exception of land.
Edit - Having gotten home and actually looked at the accounts, I thought the following were interesting:
- Transfers between the balance sheet date (30 June) and the date of signing (10 December) realised a profit of £14m. I think that pretty much confirms what we knew; Dembele, Dempsey and Dickson out for £22m and Berba, Lister and Ashkan in for £8m.
- We wrote down the value of our playing staff by £3m. I wonder if we expected to release a large number of players this summer anyway?
- Amortisation of player registrations was £17.7m.
- We sold/released players with original transfer costs of £23m. That'll be players like AJ, Zamora, Greening, Salcido, Paintsil and Gera. These players had a carrying value of only £3m at the beginning of the year.