what event caused winston and his colleagues in the records department to have to work so much overtime? also what is the purpose of the records department?

In this section, we learn that Winston has worked more than ninety hours in five days, along with everyone else in the Party, because of Hate Week. On the sixth day, the enemy changed from Eurasia to Eastasia. Immediately, all the propaganda had to be adjusted to denounce Eastasia rather than Eurasia, Oceania's new ally. Winston recalls that when the event happened, he was watching a speech. The speaker was interrupted and after reading the newsflash, continued on almost seamlessly, denouncing Eastasia rather than Eurasia, which he had been discussing only moments before. The Party worked to "correct" old news stories and propaganda about being at war with Eurasia. In the view of the Party, Oceania had always been at war with Eastasia.