Yeah, I didn't move the note. It's still in the original notebook that was created.
Even though I said "just upgraded", by the time I posted in this forum, it was hours later and as I type now, it would have been more than 24 hours since I have upgraded. I've also checked in the Account Level section to ensure I am on the Premium - I am. Yet, I checked all my notes today and the 'View History' option is not available.
I got help from Support via the live chat yesterday and they did all the troubleshooting with me, including checking that I was on the latest version of Evernote, etc... they've team member has submitted a ticket for this to be looked into. I've just got my fingers and toes crossed that they can revive that version I need quickly as the deadline for that piece of work is getting real close now and I don't know whether to redo the work or wait for a potential solution.
Thanks for your help!