Inside the "Anniversaries" modal we will find the sections "Birthdays" and "Work anniversaries".
The "Birthdays" section always displays the birthdays of colleagues in the current month. Birthdates are personal information and their display is optional. If a colleague prefers not to have their birthdate public, it won't appear in the birthday list. Similarly, you can choose not to display your birthdate and not appear in the list.
The "Work Anniversaries" section always shows the employment anniversary of colleagues in the company, including the number of years celebrated within the company.