Why is Harry thinking the word 'gotten' and where did he get it from? 'Gotten' is not used in the UK.(Check it out on the net if you do not believe me. ) The only place he might have heard it would be on an American show on TV, and he was not permitted to watch that.
Author's response
Yes, the past participle of the verb is gotten in American English. If Madame R. decides to sue me over writing this, I shall leave it in as proof that it was not meant to be a copy of her work.