So I'm one of those people that registered for CS50 last fall 2014 but never completed the course. I completed problem set 1 and logged into the cs50 website using my XID account to submit it there, but the website showed me the deadlines for the psets from last fall, not this winter/spring 2015. I'm confused about what I should do at this moment. Is there any way I can see the deadlines for this current course, and submit the psets for this current course, not the one I enrolled for but didn't finish last year?
You don't need an XID account for CS50x. You just need an Edx account to enroll in the course, which will also serve as your CS50 Submit authentication.
The only deadline for the 2015 offering of the course is December 31, 2015, by which all projects should be submitted. There is a proposed schedule for Edx students available if you need the psychological pressure.
I believe you need to re-register for this years course which is actually CS50x3. I did the same thing as you. I started in November and did not finish. Re-register for CS50x3 and you will see this years course which is a little different than last years course. If the pset didn't change, which it didn't for the scratch pset you can just resubmit it. They made a few changes to scratch and I believe the week 0 lecture is also better with explanations on using variables and incrementing or decrementing a variable.