One of Munro's greatest stories - but why did she tinker with it?

I see at least from the headline in Charles May's excellent blog on the short story that I'm not nuts (or maybe I am but not about this): that Alice Munro has made some changes in her great story, Corrie, between its New Yorker appearance and its publication in her latest collection, Dear Life. Why would she do that? I mean, either way it's a terrific story: about a smart, sassy attractive woman with a lame foot who gets involved in a long-term affair with a married man; (spoilers coming) when he reports to her that a former cleaning lady in town has spotted them as a couple and begins a blackmail scheme, the woman, Corrie, who's pretty wealthy and single, agrees to pay the blackmail. Much later in their lives, she learns that the scheme was a scam: her lover has made the whole thing up and pocketed the biannual blackmail payments and used them to help support his family. In my memory, in the original version Corrie outs him, but in the book-published version she never confronts him with the truth (nor confirms the lie), but just goes on making the payments: making the guy a kind of gigolo and Corrie rather pathetic and dependent. The story has lots of emotional twists, and it remains one of Munro's most vivid depictions of an adulterous (or maybe of any) couple - but I think I prefer the original. Or maybe I am nuts. Two adjacent stories in Dear Life make another of the Munro mirrored pair: both are about another Munro trope, the "couple" that builds a life together outside of marriage and without a sexual relationship. In Pride, a guy with a harelip and thereby a terrible self-image, is befriended by a wealthy and seemingly popular young woman, and they essentially spend their whole life together - but he, in Jamesian or a Prufrockian way, feels he has missed out on his whole life - very sad story. (The suffering of the malformed is a big  Munro theme as well, and at times that echoes Flannery O'Connnor.) The mirror story is the much longer Train, about a returning war vet who appears at a farmhouse where the woman running the small dairy farm takes him in for a night and then, following his doing a number of chores, essentially for their whole life, though again they never seem to have a sexual relationship - his sexuality is in fact somewhat ambiguous as is his whole personality. There's obviously something he's running away from - it's unclear why he never would have made contact with any family members or friends after returning from WWII - and the story (he moves to Toronto with her when she's hospitalized, falls into a job as a building super) is rather long and, at least on my first reading, very difficult to parse, with a # of typically Munro late-introduced characters and plot elements.