Why some of my Microsoft contact birthdays are not on my Android calendar?

[TheMarkNelson]

I use Microsoft People for all my contact emails, phone numbers, birthdays, and anniversaries. When I go to the calendar on either outlook.live.com or the app on Windows 10, all the birthdays show up where they should. When I link the live account to both my Galaxy S6 and Galaxy Tab S2, there are a few birthdays that don’t show up on the android calendar. But most do! And all contacts were created the same way at the same time. It would be less weird if a contact’s birthday didn’t show up on any calendar…the one at outlook.live.com, Windows app, or Android app. But why would a few people’s birthday’s show up on two of the calendars but not the third?