The license model is graded in ten-license packs.

A ten-license pack entitles to control and monitor 10 different Asterisk TAPI devices (TAPI lines).

With a ten-license pack you may install the TAPI driver also on more than 10 Computers, as long as is guaranteed that a total of maximum 10 different TAPI-Lines are used. If you install the TAPI driver for 11 PC workplaces and two of it share a phone, then a ten-license may be enough.
If you want to observe 19 phone lines with one PC, then you need 2 x ten-license. You can use these 20 licenses additionally on 20 other PCs, as long as is guaranteed that a total of maximum 20 different TAPI-Lines are used.