When repeat event ,if the month or year don’t have the day,the occurrence will postpone automatically.For example: a event repeat monthly,every 31 day every 1 month.Some months have 31th day,some month only have 30th day don’t have 31th day.In the month which don’t have 31th day,the occurrence will postpone to the first day of the next month.It’s confusing.
In outlook calendar, it will remind user when create the event "Some months have fewer than 31 days.For these months,the occurrence will fall on the last day of the month."This is much more reasonable and make sense.
Similar cases to be considered:
Repeat Yearly,every 29 day February month.
Repeat Monthly,on 5 Monday every 1 month .(For this case,outlook calendar use a drop-down list: first,second,third,fourth,last),this will prevent invalid user input and introduce confusion.
Repeat Yearly,on 5 Monday of January