When I share a photo to iCloud using the Photos app, subsequent edits to the photo in my library seem not so sync with the shared photo. Has sharing created a new copy of my photo?
Yes - sharing the photo puts it in a cloud backed "truth" where that image is available for all participants of the album to download and modify their copy, but not to change the original.
You'll want to share the edited version and then clean old ones until such time editing directly that shared image is implemented.
Photos that you share are not shared [sic], but are copied and then shared, despite clear indications in the user interface that would lead to the conclusion that they are.
Furthermore, as a consequence, albums are not shared at all: instead the individual photos in the album at the time it is shared are copied. Moreover, if you add photos to an album, and wish to add them to the shared "version" of that album, you must make sure to "share" only the added photos, as any photos that you "share again" will have new copies made for them in the shared album, and the order of the photos in the ablum will not match the order in the album that you "share" them from (the order is a frustrating combination of the order in which they are added and the date taken).
So albums are "shared" only in a marketing-speak sense.