Is it illegal to buy now, and register later?

I’m thinking of buying a digital copy of Cubase from internet resellers.

In this case, they will send me an activation serial so I can register it to My Steinberg webpage.

However, I wonder what happens if I register the serial number… let’s say 3 years later from now?

Can I just get Cubase 12.5 or whatever future version it will be then? or I only get what I purchased, so the v10.5?

Or is it totally illegal to do so?

This question is not just for pure curiosity. I’m a Logic user, but I will end up using Cubase when I join a company a few years later, and I am seeing a very compelling deal.

It’s not illegal and yes, you should get whatever version is the newest at that time. But what is the point of buying it now then and not wait until you will actually use it?

as long as they dont change the steinberg “grace period” policy you will get the latest cubase version license when activating. but make sure you buy a new license that has never been activated.
also if you are planning for few years maybe you better wait for cubase sale from steinberg,(unless you got a really good deal with 3r party retailer) i think they usually have one per year,40 % off usually. now they have discount on upgrades from lower cubase versions. they have also the competitive crossgrade price option if u got other DAW license(see a list on cubase sell page)