, где-нибудь в тексте есть упоминание первого сентября? Хоть раз?

Term begins on 1 September. We await your owl by no later than 31 July.

‘Yer ticket fer Hogwarts,’ he said. ‘First o’ September — King’s Cross — it’s all on yer ticket.

Every night before he went to sleep, Harry ticked off another day on the piece of paper he had pinned to the wall, counting down to September the first.