The Story behind ASINs – Amazon Standard Identification Numbers (2021)

That sounds like an inventory keeping nightmare! You buy 4000 units of green bananas and end the month having 0 units left, having sold none... while you somehow managed to sell 2200 yellow bananas you didn't even have and on top of that lost another 1800 (that never even existed!) to spoilage.

I heard this second hand; I don’t actually know how the inventory for Fresh worked at the time.

>Some products come from AFN/FBA with an ASIN-formatted number on a barcode on the product bag, but which starts with "X" instead of "B". I believe this to be some kind of inventory tracking code that relates the product to the vendor who shipped it into the Amazon fulfillment network.

Correct. It is an FNSKU (Fulfillment Network SKU), which is both product- and seller-specific.

Amazon listing for item with ASIN B1234567:

* Seller 1 sells on the listing. His inventory of B1234567 is assigned FNSKU X8675409. When he sends inventory to Amazon, each unit must have a sticker with X8675409 covering the UPC code, or the seller can pay a fee for Amazon to affix the sticker.

* Seller 2 sells on the listing. His inventory of B1234567 is assigned FNSKU X4894608. When he sends inventory to Amazon, each unit must have a sticker with X4894608 covering the UPC code, or the seller can pay a fee for Amazon to affix the sticker.

For most listings, the seller can choose to use the UPC code instead of Amazon assigning an FNSKU. Called "commingling", this is unwise because there is no way for Amazon to distinguish between its own inventory, your genuine inventory, and another seller's counterfeits. Amazon says that its inventory procedures still differentiate between sellers, but a) no one believes this and b) all the stated procedures would do in a case of, say, Seller 2's counterfeit item being shipped when Seller 1 makes a sale would be to potentially identify that Seller 2 is the source of the counterfeit, as opposed to avoiding shipping it in the first place.

Because you get issued a range and you actually do whatever you want within that range. Like IP addresses.

What you do within that range is up to up, you don't actually have to ask the authority for every single number within the range. As a simplification: If you get the number from 100 to 200 to assign to your books but the last digit is a check digit, you didn't get 100 numbers to choose from. You got to choose from: 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 and the third number is the check digit, which is computed from the other numbers. Just with ISBNs (and other numbering schemes) the numbers are larger of course.

Going back to the IP address analogy: if you are issued 11.0.0.0/8, you can use anything from 11.0.0.1 to 11.255.255.255 but you don't have to start with 11.0.0.1 and you don't have to treat it as one big /8 either. You can subdivide it into multiple /28s for example.

The only difference here is that with ISBNs (or anything else that has a check digit) is that the last digit is not freely usable. It's just a check digit. It's not really part of the range so to speak. It's like you subdividing your /8 into lots of /28s but ignoring the fact that the network address on the /28s is actually the network address and having one of the computers in your network use it as their actual IP address. That's obviously gonna wreak some havoc because some of your network thinks it's a network address for one of the /28s and some others think it's an individual computer.

> It’s actually worse than just not using the last digit, but I’m not getting into that here.

Clearly, using only nine characters would have been asinine.