Part numbers are the reference for the engineering definition and manufacturing process. Products have the same part number because they are the same design with the same design tolerances, are physically interchangeable and meet a minimum performance level. Due to uncontrolled variability in the manufacturing process, some products will yield different levels of performance. That performance is only able to be measured after manufacturing is complete and the product is put on a test stand. Test results, which would include a large dataset for each production unit, needs to be tracked and associated with each unit. This must be done based on something unique from the part number. A serial number is used.
That's completely untrue.
See again CPUs- where PNs are assigned
after testing.
Faster CPUs get assigned higher-end PNs, and are sold at higher prices.
Slower ones get assigned lower-end Pns and lower prices... unless there's a glut of higher performance ones in excess of demand, then sometimes they'll sell a "better" part under a cheaper PN.... (one company in that position once famously drilled holes through more expensive parts to sell them under a cheaper PN because yield of the better one was so high and demand for the cheaper one so high)
But they always BIN them by part number because that makes tremendously more sense for supply chain, repair parts, and more.
The "practical reasons" are many. There's often motivation to track product performance or maintenance over time, in field use, to help isolate variability in the production process. Serialization permits a traceable feedback loop from field experience to manufacturing with the goal to further reduce variability.
You seem to be confusing two different things.
The "many" reasons you give- which really was just one reason BTW- is a reason to HAVE serial numbers.
it's not, at all, in any way, even slightly, a reason to use them
instead of PNs when binning a product after testing it in the factory.
In fact using SN, as described, for that purpose, is demonstrably inferior to PN, as already explained in some detail.
Let's go back to CPUs again.
intel CPUs
have SNs. But they're not BINNED by them. After binning they get PNs based on what they tested at.
The SN still exists- and is still tracked- but NOT for things like replacing a part under warranty.... where PN is a
much better way to do it- and requires all parts with the same PN to be functionally swappable.
SN remains useful for things like knowing which CPUs, specifically, to recall if they find out there was a manufacturing defect during a specific production run. Also for knowing when a specific part was sold for warranty reasons (this one is less useful for a car maker of course).
But using SNs to differentiate performance? That's nonsensical and you've still given -0- practical reasons to do that instead of PN like everyone else does.
Serialization also allows part utilization to be optimized; meaning higher performing products are selected for more demanding installations.
So does PN binning.
And without making your replacement parts ordering system, or off-shelf-parts-picking a nightmare.
We have been
told by a Gigafactory engineer that the DUs are serialized and sorted prior to installation, as they should be. Product serialization is of course extremely common.
Sure, just as mentioned for CPUs.
But they don't use the same PN for parts that aren't entirely interchangeable in repair.
And nothing in the like 4 words the GF employee said tells us otherwise.
If an AWD cars DU dies, or a P cars DU dies- the same PN is ordered to replace it-or the same PN is pulled off the shelf if the SC has, as Elon claimed, begun actually stocking some parts- since that same PN was what was in the car from the factory anyway (that one weird european car notwithstanding).
Inventing a whole secret inventory system where replacement parts have a second, not-listed-in-the-actual-parts-catalog, tracking/sorting method, that appears to make everything harder/more complex, yet does not provide a single benefit anyone can articulate simply falls apart to occams razor here.
