I don't know the full extent of the distillery data available to TTB but I know that they keep track of taxes paid, using computer data of barrels filled, barrels dumped, etc. But, yes, the distillery's records would show this and the TTB probably has access to that data. They pretty much have to be able to account for every barrel for tax purposes.I get that the TTB doesn't have the resources to actively police these things, and I can grasp how easily the industry could self-regulate prior to the craft movement.
Here's a question, totally unrelated to TR: what if a producer welched on an age statement? How would it be caught? I'm not thinking so much of 6 year old juice in an 8 year old label (though that's one scenario) but rather maybe 3 year old stock in an NAS? Do the produces have to maintain records to prove such things?
As for trying to beat the reg, what many people don't appreciate is that the ability to keep secrets declines in direct proportion to the number of people who know the secret. It would be hard to put significant quantities of an underage whiskey into a product without a lot of people knowing about it. It would be a hard secret to keep.
From my experience, the majors tend to be very scrupulous about abiding by the rules because the consequences of not are so potentially grave. Some micro-producers, on the other hand, have an 'outlaw' mentality that hates authority and tries to see how much they can get away with. I imagine at some point there will be something serious that will result in a temporary or even permanent loss of license and that will get people's attention. I know the Templeton folks took pleasure in jerking me around about the source of their whiskey in the early days, so I wouldn't put anything past them.