ddenhoedLicensing does not work that way. You buy 100 KES licenses and it comes with 100 Exchange licenses. Buy 500 KES, you get also 500 Exchange.
So if you have 2 clients with 50 machines (server or workstation doesn't matter). You have a total of 100 machines. You can buy 1 pack of 100 and apply it to both clients for exchange and desktops/servers.
Pricing is definitely a little confusing sometimes, but your account manager can definitely help you out with that.