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Why do you say that this view stems from Kripke and Putnam?  Kripke and Putnam are usually taken to be opposing a broadly descriptivist view on which natural kind terms are associated with necessary/sufficient conditions a priori, instead advocating a view on which they are associated with such conditions (in the form of essential properties) a posteriori.  And while I'm no expert on Locke's complicated views on natural kinds, prima facie I don't see why he wouldn't allow that both nominal and real essences are associated with necessary and sufficient conditions.

I'm speaking of the metaphysical issue, rather than the epistemic one. Maybe you're right that Locke thought similarly (I'm also no expert), but I wonder whether we're glazing the historical narrative with our post-Kripkean brush? I'm interested because John Wilkins and I were having a beer and we were talking about essentialism and vagueness and the introduction of necessary and sufficient conditions for logical species and the extention of  this logical discussion into scientific (aka natural) kinds. We wondered if essentialism as regards natural kinds could be defended if it didn't mandate necessary and sufficient conditions. If logic needs to base our science, then perhaps a paraconsistent logic would do the trick?

Indeed, Putnam's view, in so far as i understand it, is a lot more complicated than there being necessary and sufficient conditions. He brings in such machinery as division of linguistic labour and you might, in light of his more recent neo-pragmatist developments, interpret the idea that there are a posteriori necessary and sufficient conditions for something's being a natural kind as being partially due to a decision that the linguistic community (with it's division of labour) makes. This explains why there are two sorts of jade but only one gold, and fool's gold is a different kind of thing.