It didn't -- for that matter of fact I am not sure whether it considered previous weeks, which definitely factors into the distribution. It's obviously not meant to be surgically precise, but as far as being a good guideline is concerned, I think it does an adequate job.
Players who do not play much each week tend to lose focus and their Game Shape will be sloppy. Players who play too much in a week will get tired and their Game Shape will also be low-quality. These changes are gradual, and will build up over a few weeks' time.
Massage: Players who play too many minutes in a given week will not experience as severe a drop in game shape.