My understanding, confirmed by an Evernote Expert reply to a support request, is that when I copy or duplicate a note to another notebook, and then add content to the note in one notebook, the note in the other notebook does not and cannot also update. I want the option to have the same note in two notebooks and for changes made to either version of the note to register across both notes and notebooks.
Some of my notes thematically fit in multiple notebooks and I often forget which notebook a certain note is in. My most helpful notes, like on productivity tips, and my idea lists would be most efficiently referenced if I could see them in multiple notebooks instead of looking for which notebook I put it in or using search. I thought they were syncing but now I realize I have to manually merge several of my notes. Related, a more sophisticated version of merging notes, i.e. omitting duplicate sections, would be helpful, and I see others have requested this.
Thanks for all you do for Evernote. Have loved this app for many years.