Welcome to Mobileread. Many of us are a bit obsessive about various ebook-related stuff, so you're amongst friends
I don't know what other people do, but as far as the calibre 'pubdate' column is concerned, for novels, personally I only care about what year the novel was originally written.
I don't care what year/month the ebook version was actually published unless it's a technical manual which sometimes change between editions.
At the end of the day, it's your library and you're allowed to do whatever you like.