How can the number "307703" uniquely identify a container owned by a company that "owns more than 2.4 million boxes just like it"? (SSCC-18 codes are all-numeric.)
That is why they also color-code the containers and put their logos on them.
The code is ISO 6346[1] and was defined a long, long time ago and didn't scale very well (or you could say that is scaled perfectly well - nobody imagined that 5-6 companies would control most of shipping). The container ID part, ie. the '22G1', that the article mentions actually isn't part of the ISO code and is usually printed below the ISO code. So the container needs to be identified between the top-level company ID and the 6-digit container ID, hence lots of top-level ID's for the big companies.
The whole topic of containerization and how the world came to agree on standards is interesting and has a parallel in web standards[3]. You can ship a container from Canada to Niger and know that when it gets off a ship they will have a crane to pick it up, a barcode to scan and lookup its contents, the right power plugs to power it if it is refrigerated, a way to identify the destination, owner, etc. Fascinating stuff.
[1] http://en.wikipedia.org/wiki/ISO_6346
[2] http://www.containerking.co.uk/buy-cabins/images/Shipping%20... <- see the '22G1' is printed below the ID
Worst case they just add another company code to handel the next million unventilated, 20-foot-long dry shipping container boxes.
Size and Type Codes
ISO 6346 also gives size and type codes for containers. When displayed on the container, the size and type codes shall be used as a whole.
http://en.wikipedia.org/wiki/File:Containernumber.jpg
the size and type codes aren't used in the check digit, are not required, and are usually displayed on a separate line:
http://www.containerking.co.uk/buy-cabins/images/Shipping%20...
anyway, back to the original question, you can't have two containers with the same owner code, same container ID and made unique through the size and type codes
the problem is solved because the large shipping firms (ie. the 5 or 6 that control the industry) each have dozens of manufacturing codes. see my answer in the other part of this thread
And you don't see the problem with expanding a serial number field in the middle of the code?
What tends to happen is that an 'owner' will have multiple owner codes for different subsidiaries or companies they have taken over/merged.
The containers also have a lifetime of 10-20years so presumably you can reuse numbers of containers that have been lost or scrapped.