If the "dates" are these of importing the image files into Aperture, rather than the dates on which the images were taken (from the first month january on), you are most likely right. At closer look indeed, the "consecutive sub maps" I referred to seem to be the months ("03" = march; "04" = april) and days I started using AP3.
Just remember that you are looking at the "internal workings" of the Aperture structure. That will very well change in the next major version, and it could change in a minor version, too. Basically, what you are looking at is "not for consumer use." That's why you did not find any documentation on it.