Until the realtors got to it, all of that was just Red Hook - all the way out to 4th ave, and all the way up to Atlantic. It's been a while, admittedly - but until Carroll Gardens got landmarked (and named as a separate neighborhood) there was no differentiation at all, at least in terms of what the neighborhoods were officially called (though old-timers obviously called things whatever they wanted, regardless of what the official surveyors said). If you pay attention to the OLD businesses and the signage on abandoned buildings, you can still see a lot of addresses in "Red Hook" all through the area... for example Red Hook Crushers on the Gowanus on 3rd St. Another example would be the new neighborhood Columbia, along Columbia St on the west side of the BQE - it was still Red Hook until it started getting hot a couple years ago; I remember when the neighborhood association got together to vote on what the new neighborhood would be called. See also: Nolita, TriBeCa, BoCoCa, etc.

The reason nobody knows where the borders of Gowanus are is that it wasn't even a place until a couple of years ago; I think I'm "officially" in Gowanus now, but it was the south end of Carroll Gardens when I moved here three years ago.