I came across this popup in Gmail:
when you see an underlined date, you can click it and add an event to your google calendar
I wonder why it says "an event" when it is a pretty specific event -- the one that the date corresponds to.
While I was writing this question I just thought maybe it is because in an email there could be multiple events for a mentioned date and it's up to me which one to add to the calendar.
If in another situation we're certain that there could be only one event associated with one date and a date is mentioned in the context (e.g. you can click an underlined date...) should I use "the" afterwards to speak about the event?