I'm not interested in talking about that, though. I'm interested in talking about what happens after you submit your story to the attentions of readers at large. Click below for my thoughts on what does--or doesn't--come next.
Yesterday, I noticed Simply Rarity sitting around the top of FiMFiction's feature bar, and a curiosity-inspired click revealed that Somber had just put the story onto the site and that it was enjoying its "hey it's finally on FiMFic!" resurgence (lest anyone get the wrong idea from my snark, I'm a big fan of those resurgences--they're a good way to bridge the fanfic barriers that can spring up between newer and older members of the fandom, it seems to me). Anyway, I clicked over to his profile, to find his wall peppered with "When is Project Horizons (probably Somber's most famous story, an as-yet incomplete million-word-plus Fallout: Equestria fanfic) coming here?"s, and saw this answer from another author:
Project Horizons is a work in progress. Not only new chapters are written, but old chapters are edited to fit the story to how it develops. Sometimes many changes are made across many past chapters to adapt to changes of plans.One of the big differences between professional writing and fanfiction is that, at a certain point, professional writing gets set in stone: it goes off to the publisher, who prints a bunch of identical copies of one's book, and they can no longer be altered thereafter. Now, you can still make changes in subsequent editions (Tolkien's changes to The Hobbit in order to bring it into line with what he needed in The Lord of the Rings are just one of the most famous examples), but generally you lock yourself in to what you've written well before your book actually goes on sale.
It utterly SUCKS to maintain such a huge, constantly changing bulk of text in two places, especially with one of them being FimFiction, which is not really all that friendly to uploading and editing stories.
In fanfiction (and internet-only fiction in general), though, it's much easier for the author to make alterations at any point--before, immediately after, or long past the date of "publication." This makes it easy for authors to do anything from fix a spelling error or two that an early reader points out to completely rewriting old stories to bring them into line with their later, presumably more developed abilities.
Personally, I almost never make changes to stories after I've finished them. There are a few reasons: I know that, given my personality, I could easily get caught up in constantly trying to "perfect" old stories at the expense of any other writing (or free time) if I did; I feel like a story I wrote should reflect my best abilities at the time I wrote it, and major updates would muddy that water; I would feel that I'd disrespected anyone who read the story before I "fixed" it (whether they felt disrespected or not) by tacitly acknowledging that that story I wanted them to read--that story they liked, hopefully--wasn't good enough for me to bear its association with my name in its original form. The most I'll usually do with an old story is fix formatting or technical errors, and even then I try to draw a line between "correcting a mistake" and "improving ____"--for me, the latter seems a slippery slope.
But lots of authors are more able than I am to juggle publishable with mutable. Somber obviously is able to keep writing new chapters even as he goes back and updates and modifies old ones. Of the regular commenters here, InquisitorM has rewritten Shades of Grey at least twice. And Pen Stroke's many revisions of Past Sins are well-known. I don't know how much backlash any of them faced for those decisions (I know I'd be unlikely to read for pleasure a story that I believed was going to be altered--hopefully for the better--after I read it), but obviously the vast majority of readers were fine with it.
Clearly, the best of all possible worlds would be to write a perfect story right off the bat. But, if you've published a story and now (thanks to a reader comment or the passage of time) you can see that it's flawed, what's better? To file the lesson away for reference the next time one writes a story, or to go back and bring your old story up to your new standards? I think that, more than anything, this depends on the mentality of the author, but it's still a question worth considering.