I noticed that the Verizon App 'My Verizon' now has a market update and the update seems to be following the change in fine print regarding eligibility for the double data plan. I was able to use the app on my phone to double my data plan and I can log into the Verizon site to see that I now have double data on both mobile devices. I won't be updating the app on my phone because I think Verizon had to update the app so the upgrade would no longer be available. They realized they made a mistake and allowed people to upgrade their plans without locking the contract date eligibility requirements into the app.
The Verizon Forum on their web site has an Admin who posted that people with contracts as old as mine can't update their plans via the My Verizon phone app but it's obviously untrue since I already made my upgrade through the very same app she was referring to.
Word of caution - don't update your app unless the one you're using doesn't work. If you're interested in doubling your data plan, I think it might still be possible with the version of My Verizon app on your phone prior to the upgrade that triggered a notification today. The deal ends sometime so this advice probably won't be good for much longer, but if it helps one person, then it was worth the time it took to write this response.