Why do some anniversaries of people I entered in Outlook.com show in Calendar?

[Windows Central Question]

Some anniversaries of people I entered in Outlook.com do show in Calendar

Some anniversaries do not show in the outlook-calendar on my PC's (Windows 7 and Windows 8.1). They show for some time after entering them. Later they disappear.

They do show on my Samsung Galaxy (Android).

At one occasion I litterally saw an anniversary disappear from the screen while looking at it.

 

[Laura Knotek]

Re: Some anniversaries of people I entered in Outlook.com do show in Calendar

Syncing Microsoft accounts and Microsoft Exchange accounts

To see the calendar for a Microsoft account or a Microsoft Exchange account (typically used at work) on your phone, just set up the account. The calendars will automatically show up along with your contacts and email, and your phone will sync the following events (these settings can't be changed):

Two weeks of past single-instance (non-recurring) events.
All future single-instance events.
All recurring events that have occurrences within the last two weeks or anytime in the future.

The task list on your phone will automatically sync with your Microsoft account or Outlook task list, depending on which account you use to create tasks.
Tip

Using Outlook without Exchange on your computer? You can't sync the calendar to your phone, but you can move its contents to a Microsoft account, then sync that account to your phone. To learn how, see Sync your Outlook Calendar to Windows Phone.
Syncing Google and iCloud accounts

To see the calendar for a Google or iCloud account on your phone, just set up the account. The calendars will automatically show up along with your contacts and email, and your phone will sync the following events (these settings can't be changed):

Two weeks of past single-instance (non-recurring) events.
Six months of future single-instance events.
All recurring events that have occurrences within the last two weeks or in the next six months.
https://www.windowsphone.com/en-us/how-to/wp8/email-and-calendar/sync-my-calendars