One ticket, one gig
If you paid once and stayed in one room, that is one diary entry. Splitting every opener into a separate “concert” inflates your total and breaks friend overlap.
Put the headliner as the gig. List supports in the lineup / notes. Radar’s bill tools are for capturing who played that night, not cloning the event.
When the support was the point
If you left after the opener, say so in notes and still keep one gig card — you were there for that bill. If you later see the opener headline, that is a new night with a new date.
Find search should use the artist you care about. You can still attach the full bill so the history is honest.
Festivals are the exception
A festival weekend is many sets, one event (or one per day). Do not turn Clashfinder picks into 40 extra gigs unless you want meaningless stats.
Club gigs stay simple: one night, one card, supports named. That is how a concert diary stays comparable year to year.