Unfortunately, there isn't much we can do to give you information if you don't ask for it. It just isn't possible for us to give a list to every new member as to what has and has not been done. You have one of two options:
A: You go around the forum, read some of the topics (especially the stickied ones) and get a feel for where certain things are. However, certain places (like the main web site) have sections that are outdated, so you have to be careful and check that you're getting the most recent information.
B: Ask here or through PM or in a visitors message or in an appropriate topic what still needs to be done, or if you aren't sure of something's status.
I understand that it can be frustrating to work on things and have them be useless. I spent about a month on a backsprite that became useless because the front sprite was replaced and I had to start over. Other times, sprites that I put a lot of time and effort into were tossed aside because something better showed up. So in reality, there is no "a little too late," because if you had given us your stuff even a few years ago, the stuff we have now would have been produced and displaced your work anyway. That's just what happens in projects: we take what is the best for the project, no matter how much work was put into all of the options, we can only have one sprite for each thing. But what you should try and look at is that any sprite you do wasn't really a waste since you practised your art, even if it isn't going to be useful. People here are pretty good about saying why things are bad and how they could be improved. But one way to not get any help is to complain about it. As IB said, you'll be treated as you act.
If I were you, I would do some research, get a better feel for what's going on, then ask questions, so that we know what information you have and what is still "ungiven." Then, you can focus what you want, if you think that your stuff will be good enough. If you want to improve your art in general, set yourself up a topic in the Cafe Topaz board and put up some of your stuff. I (and anyone else who stumbles in there) can give you some pointers on how to improve. Spriting isn't easy, and everyone starts out a little rough. But you can get better if you put in the effort.