Hey there!
We use the function WeekNumber(Now()) to print the week in several parts of our document which is shared widely across our department.
It turns out that there is currently some distortion between the week it prints (#2) and the week it actually is #1 which is causing quite some confusion.
Can this be fixed?
WeekNumber formula, as far as I remember, counts that week start on Sunday while IsoWeekNumber counts the week from Monday. This might lead sometimes for “wrong” week numbers. At lest not the one you are expecting to see 
I’m just here to confirm what @Marko_Petrovic said and probably were the confusion is 
.
When using WeekNumber(), you’ll get the number of the week for weeks starting on Sunday (which is the default starting day of the week in Coda which we can’t actually change).
But when using IsoWeekNumber(), you’ll still get the number of the week but for weeks starting on Monday.
So, if you’re expecting to get the number of the week for weeks going from Monday to Sunday, you should use IsoWeekNumber() otherwise, WeekNumber() will do the job .
Here is a small sample to illustrate 
Wonderful, now it works and I understand!
Thanks a lot to both @Pch and @Marko_Petrovic
You’re welcome !