Progress License

[make]

Hi there,
question about the Progress License Modell.
We have a Progress License (Tier Z1) for 20 Users (Enterprise Database).
No we want a license for 40 Users.( 20 new Users !)
I heard that its not possible to do this. The only chance to do this is to buy 20 new single lincenses.
I cant believe this. Can anyone give a tip or an adress where i can get informations about the progress license modell ?

Thanks for help.

Make