It is a different key. The steps I took to upgrade were...
Step 1. Clicked on "Upgrade" next to trial license in portal.
Step 2. Clicked on "Upgrade" in the next window that popped up.
Step 3. On the "Which license would you like to manage" page I selected Enterprise next to the 'edition upgrade' option and stuck with the 8SC option and added to cart. After in cart, finished the purchase with payment info.
After everything was complete, I now see a new license at the bottom of the "Assigned keys" list on my portal, but the old trial key is still showing for the system I just went through the upgrade process for which still shows as the Standard (free) 8SC key.
I did not just pick a fresh license, not sure why this happened. Hoping someone from 3CX will see the post and provide direction. I have 3 more that I'm going to be doing in the next couple weeks, so hoping to get this resolved so the next ones don't do the same thing.