A major theme in 1984 is that the Party is never wrong and commonly changes all past references to reflect this. Why would the Party have numbered editions of their Newspeak dictionary, as opposed to creating a new version and claiming that this had always been their dictionary (as they do for all other media)? Using any edition numbers besides 1 implies that they have made changes, which they otherwise would never admit to doing.
Even the Party has to make some concessions to reality. Sure, they can work on Winston until
Anything could be true. The so-called laws of Nature were nonsense. The law of gravity was nonsense. 'If I wished,' O'Brien had said, 'I could float off this floor like a soap bubble.' Winston worked it out. 'If he thinks he floats off the floor, and if I simultaneously think I see him do it, then the thing happens.'
But they still make aircraft for their war, and they do not have the pilots float off the ground like a soap bubble.
Better one concession with the edition numbers than risking a comrade getting an old edition and not realizing what it is.
Besides, it's a chance for the good Party member to practice his doublethink.