Geoff,
I, for one, have no problem believing Charles Banks' assertion that Yale's 5th had bunkering that was 12' below the surface of the green.
It is just a minor point but do you think Banks may have used the term 'elevated' to describe the maximum height differential between green surface and sand? When standing on the front of the green the back of it appears to be 3' or so higher than the front. Therefore, the bunkers in back may have been 12' below the green surface as Banks said with the one in front originally being 9' or so below the surface, similar to the depth of the one shown in the older picture.
Now, if it's possible that the super knocked off a foot or two of soil and pushed it over the edges when he removed the horseshoe feature this would have lessensed the slope of the banks, in effect 'raising' the bunkers by the same amount.
Now we are down to about 7' depth of the front bunker. Figure in the addition of sand for normal maintenance over the remaining years and maybe that's another foot.
I well remember being in the left side of the front bunker back in the mid '80s. The sand went up the slope a bit and the grass was very gnarly.
I don't know what all this means