Before installing the 4.1.12 Uograde I read through the benefits and noted that a Preview Function would be added....so Members could Preview a New Topic/Reply/Post before submitting it. A great feature that cuts down on a lot of editing after the fact. 

Now that my IPS Board is Upgraded, I can't find any Preview Function tied into the Repy field or anywhere to enable it in AdminCP.

Was I imagining that I read this would be an added function to 4.1.12?

The button is in the editor, but you'll need to add it to the editor through the ACP first.

ACP -> Customisation -> Editor -> Toolbars