Agree allowing for “I” to reference the most relevant unique identifier for the context of that client makes sense. Lowers the friction for users/devs and has a nice side effect of incentivizing the media publishers to support as it’s an organic mechanism for discoverability.

Source would also be useful. As just mentioned, loosening the requirements for clients is the way to go - but it points to a future where post processing to clean up, integrate, and present events is going to be required. It’s not so much a negative trade-off, just the reality of open data. Also, if certain communities want to be more strict, they’re free to do integrity checks on write. Only suggestion would be to call it ‘client’ instead of ‘source’. When I read ‘source’ I think of the publisher.