@SAFCasper If you're referring to the new program? All subscriptions can be upgraded, and when they are upgraded the new subscription terminates when the old one did.
So if you had for example, a 1 year pre-paid Exchange Online Plan 1, and you're 6 six months into it, and you want to upgrade it to Business Basic, that happens on the month anniversary, and the client pays the difference in the remaining time. Which in this case really isn't that much money because the two subs are very close together price wise. You can upgrade the subs to bigger subs AND increase the seat counts within the sub's duration at will, and none of these actions extend the sub's contracted time. (Microsoft and PAX8 as well as others have training on this for a reason, I suggest enrolling in a class!)
But yes, the discount for paying a year in advance is expected, what wasn't expected was us all getting that discount in effect for free for all this time. The new pricing makes a ton of sense, but it is still a price hike especially for month-to-month Premium users.
There however is ONE RUB here... ONLY the original seller of the first sub can do the upgrade! So if you sold it, you're good... If the client bought it direct... you're good. But if the client got their sub from someone else and you took over, you have to get the old vendor to do the upgrade and pay them. The subs are a contract, and set in stone 72 hours after purchase.
P.S. We're also getting 3yr M365 subs, but they do not offer any further discount, so I don't see the point.
P.P.S. I think partners that sold a pre-paid annual sub can still revoke the sub from the client when they leave too... I'm still trying to get detail in this space, because if I'm right it opens the door to some seriously petty crap!