I purchased Zorin 17 Pro recently, but expected to be able to use the education edition. How can I get the education edition (17) with my Zorin 17 Pro subscription?
You can't. However, Zorin OS 17 Education IS a possibility.
Zorin OS Education is and always will be a Free Edition only.
Education comes with either the Gnome or XFCE desktop environment based on user selection. Currently Zorin OS 17 Education is still in development following the release of Zorin OS 17 Core. (Zorin OS 17 Lite XFCE is also still in development).
Is it correct to say that when Zorin Education 17 is available, that updating to a Pro subscription will completely overwrite the education edition?
Zorin OS Education comes with a variety of educational apps preinstalled. Upgrading to Pro should not remove or overwrite those installed applications anymore than it would remove or overwrite any of your other independently installed applications.'
It would list as Zorin OS Pro, not Zorin OS Education.
Please review this thread for what is included in Zorin OS Education:
Its in process at the moment per official announcement regarding upgrades on zorin.com.
As I have stated elsewhere, if you have 17 Core you can add Educational software via Synaptic Package Manager which is available via Software. When launching you will be asked for your login password to elevate you to root. Scroll down the left pane until you reach the Education Section, then all the Software applications will be shown in the next pane.