No, the prompt to remove photos did not appear (because I don't have any new photos). I sync on a regular basis and I do check that box to remove photos. At this current moment I have no un-synced photos.
I am not sure what you mean: "there are probably no longer any iTunes synced photos"
All my photos should be synced thru iTunes. I never (ever) use iCloud Photos or Photo Stream.
Not sure how to test if the remaining photos are really photos synced with iTunes...I tired to do what you mentioned...but I don't understand so I did not get any results I can share and probably didn't do it correctly.
Is there a way to reset iTunes and have it verify all photos are in the library and have it ask if I want to remove all photos that have been synced?
I really do know how iCloud Photos works or how Photo Stream works. When it first came out in made a mess of all my pictures. Have NEVER used it since. I would rather stay away from this method.
Any video that would walk someone thru this particular issue and give the "proper" way to fix instead of me guessing?
Thanks for all your help!!