[NLips]

You can see any year by changing the url: https://adventofcode.com/2021

I think it started in 2015.

On the AoC website you need to provide solutions for each day in a given year to see the next day’s problem, so you can’t instantly see all the problems from a given year unless you’ve previously completed them.

You may be able to find the problems elsewhere on the net.

[forgotpwd16]

All problems are available as long as their day has come even while the event is running. But the part 2 of each problem requires solving part 1 first.

[NLips]

Hah - I’ve assumed for years that days weren’t accessible because the section of ASCII art for them is greyed out!