magical creatures - Why couldn't Harry see Thestrals at the end of Goblet of Fire?

Why couldn't Harry see Thestrals at the end of Goblet of Fire after the senseless and shocking death of Cedric Diggory?

At the end of Goblet of Fire, the carriages still appeared horseless to Harry:

Hermione turned away, smiling at the horseless carriages which were now trundling towards them up the drive, as Krum, looking surprised, but gratified, signed a fragment of parchment for Ron.

Goblet of Fire - Page 629 - British Hardcover - Adult Edition

At the beginning of Order of the Phoenix, Harry sees the Thestrals for the first time:

Here stood the hundred or so horseless stagecoaches that always took the students above first year up to the castle. Harry glanced quickly at them, turned away to keep a lookout for Ron and Hermione, then did a double-take.

The coaches were no longer horseless. There were creatures standing between the carriage shafts.

Order of the Phoenix - Page 178 - British Hardcover - Adult Edition

We know that only those who have seen death can see Thestrals:

‘Don’ worry, it won’ hurt yeh,’ said Hagrid patiently. ‘Righ’, now, who can tell me why some o’ yeh can see ’em an’ some can’t?’

Hermione raised her hand.

‘Go on then,’ said Hagrid, beaming at her.

‘The only people who can see Thestrals,’ she said, ‘are people who have seen death.’

‘Tha’s exactly right,’ said Hagrid solemnly [...]

Order of the Phoenix - Page 394 - British Hardcover - Adult Edition

A month went by between Cedric's death and the end of the spring term -- is this enough time for Harry to have truly internalized Cedric's death? Goblet of Fire indicates that Harry was in shock following Cedric's murder, but was able to relate the story of Cedric's death to Mr. and Mrs. Diggory.

When he looked back, even a month later, Harry found he had few memories of the following days. It was as though he had been through too much to take in any more. The recollections he did have were very painful. The worst, perhaps, was the meeting with the Diggorys that took place the following morning.

[...]

‘He suffered very little, then,’ she said, when Harry had told her how Cedric had died.'

Goblet of Fire - Page 621 - British Hardcover - Adult Edition

So, then, why couldn't Harry see Thestrals at the end of Goblet of Fire?

Answer

This one was answered (or one might say waved away), a long time back by JKR. She said that the death has to sink in for somebody to see the Thestrals.

From an interview with Stephen Fry in 2003:

Stephen Fry: […] Harry saw his parents die, so why hasn't he been able to see the Thestrals before?

JK Rowling: At the end of Goblet of Fire, we sent Harry home more depressed than he had ever been leaving Hogwarts. Now I knew that the Thestrals were coming and I can prove that because they are in the book that I produced for Comic Relief, Fantastic Beasts and Where to Find Them, these unlucky black winged horses.

However, if Harry had seen them then and we hadn't explained them then, I thought that would be rather a cheat on the reader in that Harry suddenly sees these monsters but we don't go anywhere with them, so to explain to myself I said that you had to have seen the death and allowed it to sink in a little bit before slowly these creatures became solid in front of you, so that's how I am going to sneak past that one.

Transcripts are available on MuggleNet and Accio Quote.