It would. The first problem is that as you slice down into the trial results the numbers of actual covid cases that you're looking at get smaller. So the statistical validity of the efficacy number gets less convincing.
The other problem is that we don't have data for what happens beyond that three to four week second dose window. Does the efficacy remain high, or does it soon tail off.
Checking some of the one dose group weekly for covid (with/without symptoms) might help answer that question quickly. As it happens, many health care workers and care home residents are tested regularly - so that might be easy.
Regular blood tests to look at antibody levels as the weeks pass might help as well. If they fall after 6 weeks, then we might get some early warning. I say some though - because as Pfizer warn they can't give a efficacy v antibody count rating, because that wasn't the trial they were running. No reason why that data can't be built now though, and again maybe that is planned in.