I had the same question, as my subscription does not expire until the end of August.
At
https://helpx.adobe.com/download-i... it says the following:
If your payment plan is Annual plan, prepaid, the redemption code term is added to the end of the paid subscription term.
Now I ordered the code from Digitec and redeemed it on my Adobe account.
I had to wait a few minutes for it to update.
Now it says my plan doesn't expire until August 2021.
Now, of course, the question is whether I could extend it again until August 2022. In theory, I would say "YES". But that wouldn't be fair in my opinion, so I'll let it go now and be happy with what I have now.