macOS Calendar List Mysterious Number

Question

My computer's Calendar.app displays two calendars: mine (DB) and my wife's (MM), shared via iCloud; both computers run High Sierra. The sharing works just fine.

But now there's a number appearing next to her calendar's name:

What's the meaning of this number "1"? And now that it's a day or two later, the number has increased to "12." I could imagine it represents new entries in her calendar, but then it should go away when I look at it...and it doesn't.

Answer 1

The arrow-into-a-tray symbol above also shows the number. When the symbol is clicked, a list appears, showing new entries on her calendar. When I click on an entry in the list, apparently to acknowledge it, the numbers decrease by one. So the numbers are notifications that a new entry or entries have been made on her calendar.

Answer 2

The number represents how many calendar items are waiting to be acknowledged. Most likely someone has e-mailed your wife a few appointments (calendar items), but she hasn't accepted or rejected them.