I'm taking a survey to see how common this word for a generously endowed woman is

I daresay most will agree that its obscurity is undeserved ... but perhaps fortuitous.

We have words enough in common use to describe "a generously endowed woman", including "voluptuous beauty" and other terms such as "bimbo" and "arm candy" which impress moral judgments on the figure [even as they impress contradictory judgments upon the eye ].

"Zaftig" leaves more to the imagination ... like a bathrobe, provocative in the right circumstances without being explicit.