E.M.I. acetates, know as "Emidiscs" due to their labels, were primarily used as reference and/or production acetates.
George Martin would use the discs to write additional scores for the songs. Likewise, The Beatles would use the discs to evaluate performance and arrangement. In a few cases, some were made for promotional purposes.

Emidiscs originate in the time period from 1963 -1968.
Earlier acetates tend to be Dick James acetates or various other labels
During the "White Album" sessions, acetates began being cut at Apple.
The dividing line appears to be "Hey Jude".
There are both Emidisc and Apple acetates of "Hey Jude".