I know overlapping events have not been possible previously. However, I see now the Calendar Entity has attributes with "checkable" states which appear to work (see screenshot):
condition: state
entity_id: calendar.ha_automation
state:
- Lighting Morning (Winter)
attribute: message
However, the "current" state of a calendar. <CALENDAR> entity seems to still only reference one event and when I tested an overlapping event, that additional event did not appear to trigger (I'm assuming this is because no EVENT is fired/triggered since while an event is "active", calendar.<CALENDAR> state does not change from "on", and thus no event is triggered.)
(Post too long; see below for researched solutions I found so far)