in one sentence you're saying that we don't have to accept that this fictional universe can be faulty, and in the next you're willing to remove this one event from the timeline due to "careless writing". Either everything that happens onscreen is canon, or we have to accept that this fictional universe contradicts itself from time to time.
But the logic doesn't work that way. If we accept everything onscreen without occassionally arguing that the characters are fallible, only then we must acknowledge that the universe can be faulty.
Of course the universe as written is faulty, because the writers aren't constrained by the rules that govern true universes: there is no inherent causality in the written universe, no rules of nature. And the writers certainly aren't obligated to create or obey such universal rules of their own. But a faulty universe is a difficult one to swallow, because those don't happen in reality...
So an "exception" has to be made in "Dr Bashir, I Presume", because otherwise the universe doesn't make sense. And thousands of such "exceptions" are made anyway, because in the average case we don't know the writer's intention and cannot divine it, but must simply adopt an interpretation of our own, which really is more likely to be contrary to writer intention than not - for me at least, as I never saw the sixties, and I don't hail from the United States, so I wear shades necessarily tinted differently from those of the writers.
Timo Saloniemi