Every drug marketed in the United States must be listed with the FDA and assigned an NDC. The number is not a licence or an approval — it is an inventory identifier. A product can hold an NDC and still be unapproved, withdrawn or under recall.
The FDA publishes NDCs in a 10-digit form with three possible segment shapes (4-4-2, 5-3-2 and 5-4-1). Electronic claims require an 11-digit form in a fixed 5-4-2 shape, which is why the same drug appears with two different-looking codes depending on whether you are reading an FDA listing or a claim.