Okay, dates are not one of my "Strong Points" ... So bear with me while I muddle through this.
As I understand in, we got 2 different Week-Of-Year (WOY going forward) standards, Simple (SWN) and ISO 8601. From what I gather reading the link you posted (thanks for that btw):
Simple = day one (e.g. Jan/1) week one. 7 days later is week 2, etc., etc..
ISO = week 1 of a given year is the one that includes the first Thursday of that year (and then it contradicts itself).
I'll clarify that last part (from the article).
In [ISO8601], the week number is defined by:
weeks start on a Monday
week 1 of a given year is the one that includes the first Thursday of that year. (or, equivalently, week 1 is the week that includes 4 January.)
Now Monday = 1 tracks with Thursday = 4 just fine (i.e. 2007), but if week 1 needs a 4th to be week one, there is no guarantee that it will come with/as a Thursday. So which is it? First week with a 4th, or the first week with a Thursday?
2007 1st Thursday was the 4th (perfect!). - Windows called it week 1
2008 1st Thursday was the 3rd. - Windows called it week 0 (but next week (was week 1, and) had 1st Thusday...)
2009 1st Thursday was the 1st. - Windows called it week 0 (but next week (was week 1, and) had 1st Thusday...)
2010 1st Thursday was the 12/31 of 2009. - Windows called it week 0 (but next week (was week 1, and) had 1st Thusday...)
Note: Both Window XP & 7 give the same answers when I pull the WOY out of local time.
So the kicker is really 2008; its got a Thursday, and a 4th (but it's Friday), and Windows called it week 0 ... Now to your way of thinking is that correct, or no?
Now I can pull SWN (as an option 2) out of the same place by grabbing Day-of-Year and dividing it by 7 (simple enough). The question is, do you think (based on above assessment/ramblings) that Windows (by default) has the ISO WOY correct? Or is there something else I'm missing/misinterpreting