what event caused Winston and his colleagues iin the Records Department to have to work so much overtime?

The event that caused Winston and his colleagues to have to work so much overtime in The Records Department was the change in war. The war with Eurasia was officially over, and the war with Eastasia had officially begun. The records department needed to do a quick fix in their department to make sure that history was rewritten to reflect the present.

The purpose of the Records Department is to adjust the records of the past to the current party line orthodoxy. Because things change on a daily basis, and because past events are consistantly erased or changed in order to align the past and present, the records departmrny is kept extremely busy. Events can disappear, and people can become "unpersons."