Things have moved on a bit since that was written. A number of Jazz Festivals have been measured and they range from 5" to 5.5" including everything in between.

There isn't strong evidence that they started out at 5.5" (picking up shells from a different model) and then changed to 5" when the stock of 5.5" shells was used up. It is a nice theory, but it doesn't explain all those intermediate depths which exist.

It sounds to me that rather than some "efficient use old parts on hand" effect at work here, it may be just that they were variable. Not to say Ludwig didn't use existing warehouse shells and parts up -- plenty of evidence for that in the more general case.

But I'd start by just describing the evidence (they were variable in depth) rather than an interpretation based on an appeal to "common sense" in the absence of actual evidence. Simply saying "they vary from 5.5" to 5" would at least put readers at ease knowing that their Jazz Festival can be original, whatever the exact height.

The next step is to test the assertion of some chronology at work by figuring out the oldest and most recent 5" and the oldest and most recent 5.5". Does the distribution heights change over time?

I'd be interested to hear from Jazzfest owners about the height of theirs if they have a date stamp (or other good date info) for it. Mine is 5.5" and date stamped November 1963 (it is pre serial number).