I've built a product that is fed calendar information, we're going through a beta test phase right now and we've found that when people have:
PRODID:Microsoft CDO for Microsoft Exchange
We see that in the case of the meeting invite being forwarded to us after the meeting has been scheduled we do not get access to the ATTENDEE rows.
Is this expected behavior? A large portion of our testing has been using Google Domains and we do not see that with them.