When a clock is ticking down, the pressure's on and you're locked-in, sometimes you miss things you otherwise never would.
Novi Sad (Нови Сад) means “New Garden” or “New Orchard” in Serbian. It has had many official names with the same meaning throughout history: Neoplanta (Latin), Neusatz (German), Újvidék (Hungarian), Nový Sad (Slovak), Нови Сад (Rusyn).
Anyway, it has always been with a single A in Serbian. If anyone had ever spelled it with double A in some other language, it must have been a really really old source. Or, it could have been a misspeling or a joke.