The Data List of Invitees for an Event Invitation appears to be limited to 10,000 records in SP20, whereas in SP13, which we are currently using, it shows at least 17,400, the highest number I think we've used so far.  It should not be limited, or if it is, this should be clearly stated so that we don't think that the number it is showing is meaningful.  Thankfully, the full number of 24,909 are sent.  We've discovered this during testing of SP20.