I believe Daniel is correct in what he says - Steinberg have never offered educational discount on version upgrades. Generally speaking, Steinberg only offer educational discount on initial purchases. With Dorico, there has always been a little more latitude than with other Steinberg products where only initial purchases qualify for educational discount. There has always been an educational price crossgrade from a competitor scoring product to Dorico (Pro). With Dorico 3, there is also an educational price upgrade from Elements 3 / Elements 2 / LE 3 to Dorico Pro 3 Educational, though this saves relatively little over an outright purchase of Dorico Pro 3 Educational.
I’ve just upgraded my Dorico Pro 2 Educational licence to Dorico Pro 3. As well as the version upgrade, my newly upgraded licence is now a retail licence with no usage or resale restrictions (as is usual Steinberg practice when upgrading an educational licence). That is a remarkably good deal for around two sevenths of the cost of a new Dorico Pro 3 educational licence and around two elevenths of the cost of a new Dorico Pro 3 retail licence. As Rob correctly points out, the cost of upgrading each time a new version is released is around the cost of the cheapest coffee in a coffee shop once per week over the approximately annual upgrade cycle. Indeed, in London, I doubt the £85 Pro 2 to Pro 3 upgrade cost in the UK would buy you much more than two thirds of a year of one cheap coffee per week.
Steinberg’s policies on educational licences are more generous than some other audio software companies. With some companies there is no way to remove all the restrictions from a licence that was originally an educational or academic licence. I have an academic licence for Cycling 74’s Max 8. No matter how many times I upgrade that licence in the future, it will always be Not For Resale.
Ultimately, educational licence policies are a matter of business strategy. Students and teachers have no absolute right to discounts, though companies understandably want educators to train those who will be entering the industry on their product, also those industry entrants to have their own copy of the product.