Microsoft
MicrosoftTeresa_Cyrus , "Follow" and "Follow up" are different things. I am not responsible for either of them, but I might be able to give you a bit more info on them.
The Follow up is a non-RSVP related functionality that you only see for past meetings. It has been there for a few years already. Once the meeting is in the past, it does not make sense to be able to respond (RSVP) to it anymore, and the Follow Up button replaces the top-right RSVP card so that you can more easily invoke some meeting related actions like "Schedule next meeting", "Reply to organizer" and "Reply to all attendees".
What was announced on last November's Ignite was Follow, a new to-be-released feature. In simple words, Follow will be a new meeting response that will get added to the existing RSVP trinity (Yes, Maybe, No):
Yes - I will attend
Maybe - I might attend
No - I will not attend
Follow - I will not attend, but I am interested in receiving info/updates about this meeting
"1) For a previous meeting, I received the follow-up Icon in the email version of the RSVP only. "
Working as expected.
"2) I don't see the Follow-Up icon in the Calendar for upcoming meetings or the email RSVP version."
Working as expected. You are not supposed to see the Follow up button there, because the meeting has not happened yet. You also don't see the new Follow RSVP/response there, because it has not been released yet.