I’ve had things like this happen before where the fare basis I am trying to rebook, actually was filed with a “travel complete by” date, and that specific fair basis couldn't be used. But that doesn’t mean they need to jump immediately to only.fares that exist today, I believe they’re able to look at other historical fare bases that would have been ticketable on the date your ticket was issued. I was able to point to a family of fares that were available at the date of ticketing and take advantage of one that was slightly more expensive that did not have a “travel by” restriction.