Week number labels should always be on Mondays and be displayed on bottom left instead of top left of days.

• Week numbers are primarily used in Europe where weeks begin on Mondays, so week numbers should increment on Mondays, regardless of when user has chosen to start their week.
• Displaying week numbers on top left of month days can become an issue if there is any kind of event on that day, but the row with the date number is completely separate from the rest of the day, so it will never have any events in it. Might as well use that empty space.