I have, in fact, worked for multiple manufacturers of serialized products.
My point is that even though there are multiple points where the serial number "should" be checked, there are also multiple points where that could fail for one reason or another.
The whole point of a serial number is to be able to track an item through your supply chain
If it can get through your supply chain without anyone ever reading the serial number, why are you putting a serial number on it at all? Decoration?