Isn't a side affect of having a single customer that has X seats at one price and Y seats at another that you now have to keep track of multiple metrics per customer (# grandfathered users, # new users, price per grandfathered user, price per new user) instead of just user count and price per seat? And for the customer to understand how they're being charged they have to be told all these metrics as well in their invoice? What happens when you raise the price again in a year or two? You now have to track 3 different user counts per customers, all with different prices?