A while back someone posted a section of the 4.1 server README file (see
below).
Says that TSM 4.1 doesn't count license as "in use" if the client has been
inactive for 30+days.

Does that mean you only need to pay for enough licenses to cover the "in
use" count now?

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$$1 License counting changes for "in use" *
********************************************************************
With this service level the following changes to in use license counting are
introduced.
License Expiration. A license feature that has not been used for more than
30 day will be expired from the in use license count. This will not change
the registered licenses, only the count of the in use licenses. Libraries in
use will not be expired, only client license features.
 - License actuals update. The number of licenses in use will now be updated
when the client session ends. An audit license is no longer required for the
number of in use licenses to get updated.