I agree with the masses.
Its probably rare that board were sent back to the factory.
However, as a company, you have to understand how a company works Logically.
A bunch of games are made in assembly lines, in a crowded and somewhat dangerous enviornment.
Not only would it be difficult to get one of the cabs off the line for testing... but, what happens when all the cabs have finished their run, and are out of the factory?
And even withstanding a lot of other related arguments... you also have to realize, that getting in and out of a cabinet isnt efficient at all. Some board mountings are not easy to hook and unhook. First you have to unlock the cab, (wheres the keys? lost keys in the process?) then you have to unlock and unscrew areas to get access to boards. TX-1 for example, has a custom metal crate that must be un-screwed in about 4 places, to open it up to get to the PCB. You also risk bending and or breaking wires on cabinets from too much in-and-out use at the factory. Also, you may make it look like the cabinet was used... when instead, it was supposed to be squeaky clean new.
Some guy was probably given this, sat in a single room, running constant tests. Either before, after, and or both. And or as said, it was probably sold to Ops who had very large routes, game mechanics for hire, and or Atari's own remote testing requirements (such as on-site arcade prototype testing).