Keys and how to tell how many PCs left on one key

I have purchased 4 licenses for Start 10 and therefore have 4 keys. I only have about 8 computers and all running Start 10. 6 have been upgraded from Win7 and 2 came installed with Win 10. Every now and again, the installation process for Start 10 (or 8) has mentioned that I needed to get a new license and I did. But now I find out that each single license can have be used on up to 5 of my PCs. I got Stardock to send me an email with all of my license codes (and they did) but how do I tell for each of those codes, how many of the 5 have been used up?

   Thanks,

Jan