I realize what you're saying about the teaching, even though it gave me a near-headache during the study trying to understand how Jesus could be present but not yet arrived as Judge.
Anyway, I think this is the key point: as you said, how can they stand up 1919 without 1914? Very easily! Wasn't 1919 when Rutherford et al. were released from prison, or when they started emphasizing the preaching work? The Society doesn't need Jesus' presence to start 5 years earlier. It could start at that time of appointment in 1919. It could not start at all!
Since Jesus is 'going away on business' in the parable, he only needs to make an appointment and leave. His presence actually works against this interpretation, not with it. The only thing the Society needs is some important event to serve as the beginning of the appointment. And if they've moved the year in the past, they can change 1919 too, if they need a better anchor year.
A good suggestion from previous posters is that the Society could actually acknowledge 586BCE as the correct date of Jerusalem's destruction, because this bumps 1914 down to 1935. Guess what happened in 1935? The "new light" about the great crowd! Yes, that's right, the distinction between the little flock and the great crowd was made in that year, which is like the distinction between the domestics and the faithful slave that this whole appointment business hinges on*. Get my drift?
*Except that the domestics now include all of the anointed remnant who aren't in the Crazy Eight, which is a detail that the Society can easily overlook when explaining all of this.