help calculating year to year commissioned payroll

So I am working on a modeling spreadsheet for a business partner and I am stuck on how to model sales rep growth and the corresponding payroll. Since commissions paid also include renewals based on previous year sales I cant figure out how to correctly reflect that in my main worksheet.

Anyway, the point of the matter is that a sales rep that starts in 2014 will not earn the same amount of renewal commissions as a rep who starts in 2016.

What I need is for this spreadsheet to adjust the column titled "Pay To Sales Reps" to correctly reflect the amount of pay going to both types of sales reps based on how many there are and when the sales staff was increased.

I know how to calculate it all manually but I would really like for it to all be automated.

What I would like is M16:M36 to display total payroll for the corresponding year but have it be dependent on how many of each sales reps there are and how long each has been at the company.

EDIT: Updated file is found in third post.

Thanks for any help!