Prior to the end of Goblet of Fire, are we ever told how Dobby got in to Hogwarts?

In Harry Potter and the Chamber of Secrets, British edition, Apparition isn't mentioned even once.

In the American edition, Apparition is mentioned, but it isn't related to elf magic. ¡Thanks @Pam for the link! https://www.hp-lexicon.org/2001/10/29/differences-british-us-versions-cs/

In Prisoner of Azkaban and Goblet of Fire it is mentioned, but nothing related to elf magic or Dobby Apparating in Hogwarts.

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I don't recall this topic being explicitly stated until Deathly Hallows, where Harry asked Kreacher how did he leave the cursed Horrcrux cave, and he is surprised that he was able to Dispparate, until Ron reminds him that elf magic is different and they're able to Apparate in Hogwarts when wizards can't.

‘But … you couldn’t Apparate in and out of that cave,’ said Harry, ‘otherwise Dumbledore –’

‘Elf magic isn’t like wizard’s magic, is it?’ said Ron. ‘I mean, they can Apparate and Disapparate in and out of Hogwarts when we can’t.’

_{Rowling, J.K.. Harry Potter and the Deathly Hallows (p. 157). Pottermore Publishing. Edición de Kindle.}