Really, I don't.
Make your lists however you'd like.
Your organizing principle can be that you have no organizing principle, only a nebulous notion of what you think came out this past year.
For my part, when I make a list, I like to know what I'm doing. Quite simply, what does "2011" mean?
My system: Trust IMDB. IMDB gives a film a date based on the best information available establishing a film's first theatrical presentation regardless of location. I like this. Film culture is larger than American Film culture. I may not be able to see all of these films, but I recognize that they exist and that they were actually screened somewhere. I might not see a 2011 film until 2014. That doesn't make it a 2014 film.
Most critics follow the NY/LA system of the Academy. If a film was released and played a week in NY or LA, then it qualifies. One problem with this is that you get the Army of Shadows effect. A film from the 60s that never ever got a theatrical release in the U.S. now qualifies as a 2006 film because it played in the U.S. for the first time in 2006. More often, it's not this drastic, but it's often the case that films from the past few years are only just now getting to us to qualify.
Another problem is that NY and LA aren't really any more relevant to my movie-watching life here in the Binghamton area than Cannes or Berlin are relevant. All four of those cities are too far away for anything played there to matter (okay, I could drive to NY if I REALLY wanted to see something, but practically, this never happens).
The above is fine for critics in NY or LA, but what's a guy supposed to do in Binghamton, NY? Why follow the critics when most of those films never played anywhere close to here? Why not modify our personal lists to reflect only the films that opened within an hour's proximity to Binghamton?
Why not just rank every movie I saw this year regardless of what year it is from? I mean, they're all new to me, right?
I've already made these arguments plenty of times and more fully than I do here. I'm happy with my system. I think that it makes the most sense. I won't fault anyone for using any other system. I'll just pick on them a bit, all in good fun, and only to amuse myself and to continue the running film dating joke that has begun here.
Whenever I do "get on someone's case," it's only me being playful. I'd love for everyone to agree with me, but I'm not really getting upset or worked up over the fact that no one agrees with me.
I guess all I'm really fighting for is for everyone to pick a method, clearly describe what that method is, then stick to it. My method is best, but you can pick your own. :)
Is it arbitrary to rank films by year? Sure, but once we've decided to arbitrarily rank films by year, let's at least be clear about what we mean by a year.
All that said, you make really good points about time being the most necessary ingredient in proving a film's worth. I agree. Well said. No insults.