Yes. Some are destroyed. Some are lost. Some wear out. Some are illegally exported.
On the other side:
Some are homemade and not counted.
Military arms, originally sold to the military, the transferred to civilians, by various mechanisms, are not counted. (several million were sold surplus in the USA)
Guns illegally imported are not counted.
Because these numbers are so difficult to know, the assumption is they off set one another.
Fascinating info...