In #4017 (comment) we added RawEGI.event_id which disappears on round-trip. This is due to not knowing which/how many DIN channels will get triggers.

Nowadays we should use Annotations rather than synthesize an event channel I think. Not sure if it's worth keeping the event channel synthesizing around for backward compat or deprecating it. But either way adding the annotations will make it possible for people to use modern code rather than relying on raw.event_id here.

See also discourse for discussion.