Only new episodes will show as updates. Existing episodes that have been updated with added pages will not, and in my opinion are more annoying to navigate through than a bunch of single pages, because tapastic will not save your place in an episode, so you have to scroll through the chapter and find where you left off.
Additionally it also give you another problem which leads to readers ignoring updates or even missing content and jumping to the next episode and not finishing the last one. This issue popping up because the edited episode notification doesn't go into their 'comic notifications' list where they usually get their updates. It goes in the activity list. (this makes it even MORE miss-able to users that have their own comics as well, as it'll be burred along with the comments and likes for their own comics and is very easily missed)
Something you can try that seems to work for people is to upload each page as an episode, and then when you have enough pages for another '25 page episode' condense all those pages into one. Unfortunately you will lose all your comments with this method.