I decided to start from scratch... This is what I came up with:
(calendar.EventDate = DATE_ADD(CURDATE(),INTERVAL 1 MONTH))
OR
((DATE(calendar.DateAdded) = CURDATE()) AND calendar.EventDate BETWEEN CURDATE() AND DATE_ADD(CURDATE(), INTERVAL 1 MONTH)))
The logic is:
(calendar.EventDate = DATE_ADD(CURDATE(),INTERVAL 1 MONTH))
(the event starts exactly one month from today)
OR
((DATE(calendar.DateAdded) = CURDATE()) AND calendar.EventDate BETWEEN CURDATE() AND DATE_ADD(CURDATE(), INTERVAL 1 MONTH)))
(the event was added today) AND the event is between today and one month from today