Hmm, at this point think it would be best to just look at the example. It's not too big and I leave it to your team to figure out how to extract a test case.
The "add" use case is important, because even if the existing items are live updated, any new items also need to reflect updated values. Furthermore, when there are subsequent updates the added items must also be updated. Maybe this falls out of the eventual solution, or maybe not, but this does not work in the example either.