Wikipedia tells me that the first known usage of "zero" in English was 1598, certainly well after the rules for plurals were set.

Wikipedia also tells me that people started speaking what we now call Old English around 450, and also tells me that there were examples of something close to the idea of "zero" going back as far as 1770BC, although the usual history of "zero" in English just goes back to borrowing it from Sanskrit, where it might have first appeared as early as ~300±80 but definitely appeared in 458.