I think we can. Had closing happened more like it was a few months ago, by the time it closed, got recorded, got to DVC and DVC set up the account, it would have been a full month from now even with the date it did close and were DVC not moving faster than before, it would likely have been an extra month before closing occurred anyway.
For a reservation within the window it's generally taken to get through the system, I don't think it would or should have made any difference for reasonable people. Certainly for something that would truly delay a reasonable closing, that's different and is 100% not the case here. Likely what the seller should have done and could have done legally, would be to simply have delayed sending it back a couple of weeks and if it came up, explain why.
For something so close, it should not have made a difference to anyone. The ONLY way it might have possibly made a difference was for 2 or more essentially identical contracts where the buyer was deciding between them. And who's to say the buyer didn't get a better deal because of this, we simply don't know and never will unless the seller pops in and addresses the issue.
Your explanation makes it worse to me.
1. If closing had gone like they used to go, this wouldn't have been discovered.
That would suggest a strategy to maximize selling during prime summer seller market while taking a vacation during the same time and trying to avoid being penalized financially for doing both. It would also suggest purposefully withholding a material condition of the contract.
2. The seller could have waited to sign but didn't. And by not disclosing, the closing already happened. They jammed up the buyer and broker (and closing agent and DVC) by trying to ride it out.
3. At this point, it doesn't matter when the closing was promised; it's already happened. At issue isn't the already transferred title, but the transfer of the account by DVC.
You say that it's 100% the case that this trip shouldn't affect promised closing, and I guess that's right since the closing already occurred. But it DID affect the transfer of benefits.
The buyer should have been allowed to decide if they wanted to entertain any potential aggravation that a scheduled trip would have - and ultimately did - involve.
And I agree with the above that it bothers me that the disclosure happened after the buyer's most convenient remedy - backing out - has passed. And it bothers me that the broker is leveraging that lack of buyer's remedy to apparently do nothing.
I just don't think the rationale that it's not a big deal because the seller might have gotten away unnoticed with a self-serving contract violation if DVC had just been less efficient is a very convincing justification for the aggravation the OP is currently experiencing.
It reminds me of Scooby Doo, "And we would have gotten away with it too, if it weren't for those meddlingly efficient cast members at DVC!"