I've just had word from arcum42 that some updates of chapters aren't coming through. After a little bit of wondering, I think I've found why this is and why his suggested solution works.
While I was writing this thing, I kept the story unsubmitted, but published certain chapters for pre-readers. I then also added passwords for the unpublished ones, to make sure that everything was in order.
Here's what I think happened: when you publish a chapter, you send one signal that determines whether or not this counts as an update. If your story isn't submitted, it doesn't count as an update and the opportunity is lost. So if you unpublish and publish again, it doesn't send another update and the chapter isn't put on the front page. I did a quick look at the FAQ, and if this is explained there I missed it. Bottom line is: the mods do not want people who keep bumping their story up by adding and removing the same chapters. If the site works this way, that easy abuse is automatically avoided. What I did here wasn't against the rules, technically -- since an unsubmitted story doesn't hit the front page to begin with -- but may be interpreted as such by how updates are coded.
So, if you have finished your story and published chapters before submitting, and you notice chapter updates aren't being communicated to your readers or put on the front page, here is the solution arcum42 suggested to me.
-copy the entire content of the unpublished chapter in question.
-start a new chapter with the same stats, text, title and whatnot.
-publish this new chapter. Since this hasn't been published, unpublished and republished, the site will recognise it as update-worthy.
-delete the old one, if you feel like it. Keeps things organised.
Do NOT use this to bump your story endlessly with the same chapter. It is against the rules for a good reason. Regardless of whether or not the last two updates on Changeling Blood have been registered, I'll only do this for future chapters. I'll make sure to set up my chapters today and upload a new one this Sunday to check if that changes anything. Thanks again to arcum42 for pointing this out.