I don't have an answer to your question, but I can add one data point until someone else adds a real answer: I received my Shapeoko in April 2017, and it does have the new Z plate.
It was in Summer 2016 --- not sure of the cut off date.
It's in a hidden page in our shop: https://shop.carbide3d.com/products/shapeoko-upgrade-z-axis-plate
and this PDF should allow you to determine which you have: http://carbide3d.com/files/s3plateupgrade.pdf
Rather than the new plate, you can reinforce the one you have.