Any spare part will inevitably become obsolete. This fact is not influenced by how you manage your inventory or how well you train your team. Technology changes, designs change, equipment changes, processes change — these are things you really cannot expect to influence to any great extent. What you can influence, however, is how you plan for and respond to obsolescence, whenever and however that occurs.
There are many labels used to describe obsolescence and how the obsolescence comes to be. For example, sometimes the phrase “commercially obsolete” is used to mean that the item is no longer sold. Or a part could be described as “technically obsolete,” meaning it has been superseded by newer technology. Whether this makes the item obsolete in any operational sense depends on whether you can still acquire the item when you need it.