Of clients (business clients) or for yourself (store stock)
We don't stock software...so that's a non issue, only software on our shelves will be mis-orders (like an extra office license was ordered by mistake and is available.
For our business clients, their Microsoft licenses are tracked via microsofts volume licensing, since most Server and Office stuff we purchase through Microsofts volume licensing, and it's all viewable in our portal.
For other inventory, N-Able reporting.