Huh! I don't recall ever seeing the spelling stanch & I think I'd have noticed it, since my eye stumbled over every occurrence in the paragraphs above. I've worked as a copy editor (twice) & proofreader, & read thousands of books (almost all of which were published in America). I've also read a variety of American literary & general-interest periodicals over the last 40+ years, & a number of medical texts & journals for the past 10 years. I believe stanch is a very uncommon variant of staunch in U.S. standard English spelling.