Merge plus tracking source?

Update: Just writing this out for you guys & gals has given me the clarity I needed! I’m adding a field for “source”, will merge the 2 lists and duplicates will have the merged orginial changed to “both” or something, then every other object will have it’s source attached.

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Original questions.
I may be making this way harder than it is, but I have two sets of information in an array of objects, some of them are the same and some are only in one of the two lists.

Each array comes from a different back end source (eg. like a product manual and a client handbook). As edits are made to one, they may not be updated in the other.

Going forward we’ll implement a system to avoid this but at present here is what we want to do:

Create a merged list of all the objects, and update each source.

unfortunately it’s not oas simple as copying the merged list to each source, or even pulling the lists from a single source, due to different software being used for each.

Updates will have to be made manually once the items are identified. So I just need a way to merge them then tag the items that only appeared in one list but not both.

Ideas… assign each object a counter value of 0, and if that object already appears in list A, assign it a value of 1, if it appears in list B assign it a value of 2. Or something like that?

Then I could filter for counters of 1 and use that to update list B. And vice versa to update A.

Does that make any sense?

This is for an outside project but seemed like a good algorithmic puzzle to me. Again maybe I’m overthinking this…if there is an obvious faster way to do it, let me know!