In my company, meeting requests are circulated for all meetings, and we all use the same Outlook version.  This ensures secretaries can manage their bosses diaries much more effectively...well that's how it's supposed to operate.

It was a bit unusual on this occasion since the individual, who is PA to our Deputy CEO, sends meeting requests for other meetings.

I would never send a meeting request as an email.  An email can be read and forgotten but a meeting request usually gets a response of some sort.

PS.  The first thing I do when organising a meeting is check if there is a room available.  If I omit that you can be sure I will get 101 replies asking where the meeting is being held.  Plus, my boss always needs to know where he is required to be next, and so do I.