My team's calendar's are not syncing past two years ago

Hi,

I have a number of users with my business's 365 account. I have shared calendar's owned by my user account with them. They cannot see calendar entries on their outlook apps on Macs or by logging in to their accounts on a browser, for prior to July 2019. I need them to access these to build a new customer database. I can see all the calendar entries on those calendars from my login (I'm the administrator) so I know they're still there.

I've tried searching for solutions online but nothing seems to make sense. Can anyone help please?