Snape realmente deu a Umbridge uma poção falsa de Veritaserum que Harry mais tarde fingiu beber?

Do capítulo 28, 'A pior memória de Snape':

BOOM!
The very floor of the office shook. Umbridge slipped sideways, clutching her desk for support, and looking shocked.
'What was — ?'
She was gazing towards the door. Harry took the opportunity to empty his almost-full cup of tea into the nearest vase of dried flowers. He could hear people running and screaming several floors below.

(O "BOOM!", Para o registro, era Fred e George disparando fogos de artifício.) Quanto à parte falsa - para começar, parece bastante provável que Snape fosse um espião e também odiasse Umbridge tanto quanto qualquer um. Além disso, no capítulo 37, diz

“Harry, you know that Professor Snape had no choice but to pretend not to take you seriously in front of Dolores Umbridge,” said Dumbledore steadily, “but as I have explained, he informed the Order as soon as possible about what you had said. It was he who deduced where you had gone when you did not return from the forest. It was he too who gave Professor Umbridge fake Veritaserum when she was attempting to force you to tell of Sirius’s whereabouts...”

Outra passagem relevante é do capítulo 32, 'Out of the Fire':

'Ah, Professor Snape,' said Umbridge, smiling widely and standing up again. 'Yes, I would like another bottle of Veritaserum, as quick as you can, please.'
'You took my last bottle to interrogate Potter,' he said, surveying her coolly through his greasy curtains of black hair. 'Surely you did not use it all? I told you that three drops would be sufficient.'
Umbridge flushed. 'You can make some more, can't you?' she said, her voice becoming more sweetly girlish as it always did when she was furious.
'Certainly,' said Snape, his lip curling. 'It takes a full moon-cycle to mature, so I should have it ready for you in around a month.'

A passagem que menciona Harry despejá-la está no Capítulo Vinte e Oito de Ordem da Fenix:

She was gazing toward the door; Harry took the opportunity to empty his almost full cup of tea into the nearest vase of dried flowers. He could hear people running and screaming several floors below.

A passagem mencionando que Snape havia falsificado a Umbridge está no capítulo trinta e sete:

“Harry, you know that Professor Snape had no choice but to pretend not to take you seriously in front of Dolores Umbridge,” said Dumbledore steadily, “but as I have explained, he informed the Order as soon as possible about what you had said. It was he who deduced where you had gone when you did not return from the forest. It was he too who gave Professor Umbridge fake Veritaserum when she was attempting to force you to tell of Sirius’s whereabouts...”