Here's my understanding of the process (it's probably an oversimplification, but it may help)... The design has to start out on paper (presumably a design document of some sort, followed by component selection and board layouts and so forth), but it can't jump straight from paper to mass production on an assembly line, so you have to build a few samples first. Some of the earliest samples may simply be mock-ups (empty or nearly empty shells with front and rear panels laid out but little or none of the "guts" inside). Complete, working test samples would have be built at some point, and they would then get picked over and re-done a bit to get things shaken out properly (possibly over a couple generations of test units). it is samples like this that I would expect to be used for beta testing once the design is far enough along. Only once the hardware and software is locked in would the factory start a full-blown assembly line to crank out large numbers of units. Until that assembly line kicks in, any samples that are rattling around (in-house testing, external beta testing, trade show demos) would be what I'd call "pre-production".