The license pool is supposed to map the purchased licenses from the view of your buyer, not from the view of appearances in your network. So, if you have purchased a set of 50 Office licenses in january then you will use the license pool to enter a license record with 50 Office licenses. If you then purchase a set of 50 further licenses, you will add another record with 50 using the same license name. The Lan-Inspector will calculate 100 Office licenses for your balances then, but you keep the information of your real purchases like purchase date of the first set of 50, etc. The Lan-Inspector will sum up your licenses correctly to be able to create your license balances. In order to do this, it uses a very complex algorithm that respects multi package licenses, upgrades, downgrades, time limitations and other aspects of license management.
License balances and reports are described in the manual here, see 6.5.2 License Balance.