What is the provenance of this Harry Potter and the Chamber of Secrets quote

Question

In a couple of answers that have been posted on this site today (one, two) a quote has been used (to good effect, I hope the authors of these answers know I don't mean to slight their knowledge of Harry Potter!) which I do not recognise:

"But your Mum and Dad..." said Harry, pushing against the barrier again in the vain hope that it would give way. "How will they get home?"

"They don’t need the car!" said Ron impatiently. "They know how to Apparate! You know, just vanish and reappear at home! They only bother with Floo powder and the car because we’re all underage and we’re not allowed to Apparate yet..."

According to a comment this appears in the ebook version, but I'm pretty certain it's not in my Bloomsbury edition:

'It's gone,' said Ron, sounding stunned. 'The train's left. What if Mum and Dad can't get back through to us? Have you got any Muggle money?'

Harry gave a hollow laugh. 'The Dursleys haven't given me pocket money for about six years.'

Ron pressed his ear to the cold barrier.

'Can't hear a thing,' he said tensely. 'What're we going to do? I don't know how long it'll take Mum and Dad to get back to us.'

They looked around. People were still watching them, mainly because of Hedwig's continued screeches.

'I think we'd better go and wait by the car,' said Harry. 'We're attracting too much atten-'

'Harry!' said Ron, his eyes gleaming. 'The car!'

'What about it?'

'We can fly the car to Hogwarts!'

'But I thought -'

'We're stuck, right? And we've got to get to school, haven't we? And even underage wizards are allowed to use magic if it's a real emergency, section nineteen or something of the Restriction of Thingy ...'

Harry's feeling of panic turned suddenly to excitement.

'Can you fly it?'

'No problem,' said Ron, wheeling his trolley around to face the exit. 'C'mon, let's go, if we hurry we'll be able to follow the Hogwarts Express.'

And they marched off through the crowd of curious Muggles, out of the station and back into the side road where the old Ford Anglia was parked.

Harry Potter and the Chamber of Secrets - pp.55-6 - Bloomsbury - Chapter 5, The Whomping Willow

And that's ... all I've got.

What's more, the missing quote doesn't sound like Jo Rowling to me, I thought it might have been a fanfiction addition or something. But if it appears in the ebook version, perhaps I am wrong and it was added in in later editions by Rowling herself (or missed out of earlier ones?)

Does anyone know where the missing quote is from and why it doesn't seem to be in my paper edition?

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Edit: rand al'thor has done the hard detective work and closed this case, but while we're all here, I might as well ask the follow-up - why? Why put it in?

Answer 1

This was inserted into the Scholastic (US) edition and does not appear in the earlier Bloomsbury (UK) edition. See page 264 of The Ivory Tower and Harry Potter: Perspectives on a Literary Phenomenon:

In Bloomsbury's Harry Potter and the Chamber of Secrets, just after Ron and Harry find themselves blocked from entering platform nine and three quarters, Ron suggests flying the car, an act which, he insists, would not violate any wizarding laws. As he explains, "Even under-age wizards are allowed to use magic if it's a real emergency, section nineteen or something of the Restriction of Thingy..." The next sentence registers Harry's interest in the idea: "Harry's feeling of panic turned suddenly to excitement." In contrast, Scholastic's edition inserts a brief debate in between Ron's passionately vague justification and Harry's excitement:

"But your Mum and Dad..." said Harry, pushing against the barrier again in the vain hope that it would give way. "How will they get home?"

"They don’t need the car!" said Ron impatiently. "They know how to Apparate! You know, just vanish and reappear at home! They only bother with Floo powder and the car because we’re all underage and we’re not allowed to Apparate yet..."

Harry's feeling of panic turned suddenly to excitement. (Chamber of Secrets, S 69)

Harry's objection reinforces the notion that Harry is more mature and less likely to act on impulse than Ron is, but it also introduces the magical skill of Apparating.