I have a question into SS support now about the difference between earnings from new content in the last year and a set of all my images accepted in the last year, but other than saying that the earnings reported is correct and if the graphs are off then they are wrong , they haven't answered.
Actually, I don't know about the earnings from new content - they might be correct for all I know, but the earnings from sets does seem to have a problem, in that a set of all my images uploaded in 2012 had a higher total than the earnings from images uploaded in the last year. (this number was off by more than the sales of new content in the last week, so it appears to be something more than the lag). Also I made a set of all my images and the total is over my total non video sales. So maybe the problem is only with sets and not with the total earnings or the earnings from new content numbers.
My earnings from new content were a much higher percent of total earnings back when they first introduced this. Partly this is because I have more old content now, and partly because I am submitting a little less, but it has dropped by more than these changes would account for.