Etymology of "nine-edge" and "twelve-edge"

Leafing through A Fortran Coloring Book (Kaufmann, MIT Press, 1978) I came across this passage, describing punch cards:-

There are twelve rows that go across each card. For reasons known only to Thomas Watson or God, the TOP row is known as the 12-edge, and the bottom row as the 9-edge.

We are further informed that Thomas Watson's will is alleged to state that he requested to be buried 9-edge down.

Aside from the intrinsic improbability of the will story, does anyone know why the edges of punch cards are named thus?

There are 12 positions that can be punched in each column of a punched card. The lower 10 positions represent the digits 0 through 9. The top two positions (zone punches) are called 12 and 11. Thus, the top edge of the card is referred to as the "12 edge" because it is closest to the 12 position, and the bottom edge of the card is called the "9 edge" because it is closest to the 9 position.

The thing about Watson's will reminds me of this verse from the poem "The Last Bug":

He died at the console,
Of hunger and thirst.
Next day he was buried,
Face down, nine-edge first.