If You Are Using iBooks, iBooks Reader for Mac, or Adobe Digital Editions:

Be aware that all of these readers, along with any Adobe Digital Editions-based eReaders (Yes, I'm looking at you, NookReader!), have issues with  caching.  What does that mean?

That simply means that if you open Version 1 of your eBook, in any of these, and then later download and try to view Version 2, there's a significant likelihood that you'll still be seeing Version 1.  The only way to ensure that this does not happen is to make sure that you've deleted Version 1 from your Library or Bookshelf, in the eReader, before you load Version 2.

If you open your ePUB, and instantly think, "hey, you didn't make any of the changes I requested," check to make sure that you're not viewing Version 1, please, first, before writing to tell us that we screwed up. Oh, heck, we could have screwed up—but please check to be sure you're not viewing a cached file, first.  

Thanks!