A New Era in Boxes?

Recently, reports have come in (Thanks, Tim S and Barry!) of new amazon box sizes. The 20 and the 70.

While Amazon Box 20 appears to be a replacement for the aging but popular A3 box, Amazon Box 70 is a new size.

A Catalog of Amazon Box Sizes

Both the 20 and 70 have the same height and depth (about 6 inches x 5 inches), and only differ in length (9 inches and 18 inches).

Is this part of a new series? Are there 50s out there? Box 40? Let me know if you know.