The rubber bands weren't holding the money together for all those years, the surrounding sand was.
I'm wondering if they were digging a fire pit you would think once he disturbed the money the bands would of fell off, and not even noticed? kind of leaves the question, "are you sure this is what happened" ? 
just a though.....
I may be speaking out of school on this, so I'll have to check, but I was under the impression that the bills were stuck (clumped) together and the rubber bands crumbled when touched.
Once the money was encased in sand, the rubber bands would no longer be needed to hold the bundles together, they could deteriorate and fall apart with no effect on the bundles.
Based on rubber band events in my closet, even after the bands break they will probably still stick to whatever they were wrapped around. And sometimes the broken bands are stuck so well that they are difficult to remove completely.
Good point! And 'that' is the infamous 'gooey' or 'melt (glass) transition stage' we are all familiar with. It can become a beautiful phenomenon like sap or amber! Wants to stick to and can even encase whatever it comes into contact with, including particles blown by the wind or forced into it! A potential forensic goldmine! Except, the temperature has to be high enough to allow this natural state to evolve. It's just glorious in its potential ramifications. Those bands could have had one helluva a story to tell ... or zip nothing too. That is why I wanted Tom or somebody to see those band fragments! Now, picture those bands turning gooey, if they ever did, on the fibers which comprise the paper of a $20 dollar bill. That 'gooey stuff' sinks down into those fibers. Now we have future crystalised band fragments-segments literally stuck to the money paper itself. Hard to pluck off at some future date when a kid finds that money and mom and Dad try to clean it up for presentation to a bank. "And we had to pick some of those pieces of rubber band off", was the statement Ive heard. And the whole phenomenon is a "clock".
Now, if it turns out those Cooper bands never went through their natural gooey stage which happens at room temperature that could imply a cool environment for the money especially during the first several years after the hijacking.
Those band fragments may tell a story that is worth knowing.
[edit] I sit here and say things like the above knowing full well this could all be pure speculation and wishful thinking. But, so far as I know nobody has looked at the band fragments to know and until somebody does look at them, we won't know. The bands could also be just one more dead end in a case of dead ends! It is a fact the bundles of money were wrapped with rubber bands, each bundle, by _______________ at the bank. Larry put forth considerable energy nailing that down and documenting it. ....... and as Tom suggests, the bands could be an important element in this case or not so important, as the case may be.
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