I'm set to auto-update, scheduled for weekly checking.
When I manually attempted to check ("Help | Check for updates" menu item in Outlook for Mac 15 menu bar) I only found update for Office 2011 (14.4.7). <have the screenshot>
Applied it. Attempted activation which failed as before. <have the screenshot>
Wasn't able to find an "update" for Outlook for Mac 15.x anywhere, so went to the MySoftware page on the portal and clicked the "Install" button under the "Get Outlook for Mac" section, which appeared to download the full app install.
Installed over my existing installation, launched, confirmed version 15.4, and was able to successfully activate finally.
I'm confused about MAU for this product and how I should know about and accomplish updating Outlook for Mac 15, but appreciate your assistance and that I am finally up and running again.
Thank you