You have to remember that it's how many players you sold in the last 14 weeks, not how long ago did you sell a player.
So for example, if you sold 3 players on Oct. 6 and one player on October 13 then:
On October 31st you would have sold 4 players in the last 14 weeks
On December 1st you would have sold 4 players in the last 14 weeks
On December 27th you would have sold 4 players in the last 14 weeks
On Jan 15 you would have sold 1 player in the last 14 weeks
So a week passing will not automatically increase the percentage of sales you will get.