problem with calendar

I have a calendar in my workbook that is supposed to be able to change the week of the year and display the date. So 9th Monday would be 2/26/2018. This works great when using week 1 through 9 but goes to pot when 10th week is changed. When I put in 10th Monday Excel is seeing 10th as the 1 week and displaying 1/1/2018 instead of 3/5/2018
any ideas how to change that?
Please see the example i have provided