That claim was never made, but by you. The claim was, Minsky had practical experience and wrote about experiences with gradient descend (aka "hill climbing") and problems of locality in a paper published Jan. 1961.
On the other hand: who invented "hill climbing"? You've contributed nothing to the question, you've posed (which was never mine, nor even an implicit part of any claims made).
Well, who wrote before 1952 about learning networks? I'm not aware that this would have been already main stream, then. (Rosenblatt's first publication on the Perceptron is from 1957.)
It would be nice, if you contributed anything to the questions you are posing, like, who invented gradient descent / hill climbing or who can be attributed for this? what substantial work precedes the writings of Minsky on their respective subject matter (substantially)? why was this already mainstream or how and where were these experiments already conducted elsewhere (as in "not pioneering")? Where is the prior art to SNARC?