The short answer is all items that are going to be brought into the inventory and managed as a stocked item. Naturally, there are exceptions but generally, all items brought into the inventory, at whatever level, should be codified. Even if an item is not brought on charge, if it needs to be managed, it should be codified. In theory, the supply system should not handle demands if they don't use NSNs, or it should have a built in auxiliary process to get codification performed before handling the demands. The same is true for other logistics systems; unless they are based on NSNs, they will not operate effectively when linked with other systems and more so when linking with systems of other NATO nations.
There are some that argue that Commercial off the Shelf (COTS) items should not be codified, but how do you ensure you are not buying something that the next unit is trying to get rid of? How do you ensure the items are not already in stock? How do you ensure you get the best deal for your money? The decision not to codify needs to be made at the appropriate level if a nation wants to reap the benefits of the NCS.
As mentioned above, there are exceptions. There are items managed by the armed services that may not require codification. Items that are acquired by a single entity for a specific purpose need not to be codified. Naturally, as soon as more entities start acquiring the same item or that there is a need to store some reserve items, than the item should be codified. If you don't, you are probably paying more than you should or are buying items that are already in stock somewhere. Again, the decision not to codify needs to be made at the appropriate level if a nation wants to reap the full benefits of the NCS.
There are definite benefits to codify Commercial of the Shelf items. If they are used by more than one organizational entity, consideration should be given to codify them.
The task of adopting the NCS is made easier by the fact that a huge number of items have already been catalogued. There are approximately 17 million items codified in the NCS. For example, in the United States has 7 million active items in their central catalogue. If New Zealand acquires U.S. equipment, then we are generally able to draw the catalogue data directly from the NCS. Similarly, if we buy French or German equipment we also draw catalogue data from of the NCS .