Avigo doesn't seem to be returning the correct numbers for Week: and Weeks Remaining: in the Calendar application.
There are many different ways to calculate the week of the year. Avigo uses the same algorithm as Lotus Organizer 97 to determine Week and Weeks Remaining. In Lotus Organizer, In order for the first days of a year to be considered a week, the first four days must actually fall in that week.
Let's use December 1997 - January 1998 as an example. On Avigo, you can choose Monday or Sunday as the beginning of the week, but Sunday is selected by default. If we have Sunday as the beginning of the week, the following occurs:
According to the rules we've set, January 1st does not fall on the first week of the new year. Only 3 days, not 4, fall inside this week. So, it is listed in the 52nd week of 1997.
However, if we have Monday as the beginning of the week, the following occurs:
Here 4 days of the new year fall inside the week, so it is listed in the 1st week of 1998.
This will explain why the week count may not match what you may expect for some years.