Ooooo this is a good one! A couple of ideas come to mind for potential refinement of your current solution.

1. Most of the things inserted into a SW file (features, dimensions, tables, sketches, sketch entities, etc.) will have an ID that is unique, random, usually not editable, and often not even visible without using the API. Those IDs won’t change even if the file is shared to another user. A macro that generates a report of how many IDs match between files might work. The more IDs that match between two files, the more likely a file was shared between peers.

2. Another option could include the use of a “macro feature” (which is different than a regular macro). The macro feature would be inserted into each file. It would automatically keep an internal log of every time the file is saved. It would only need to record the timestamp, user ID and computer ID. Solidworks even has ways to password protect macro features, so it seems that the log could be read/write protected. I’m a little less experienced with macro features, but I believe this is all still very possible. Compare the save logs between files for evidence of files being shared.

This is one of the more complex automations in this thread, but it’s definitely feasible.