If you buy ground beef at a supermarket or online, it almost certainly comes from what the industry calls the mix. The mix is what is left after the premium cuts are taken off the carcass. That trim goes into large vats holding meat from roughly a dozen to fifteen animals at a time — and that is true of conventional beef and of most retail "grass-fed" and organic beef too.
Do the arithmetic. If you eat ground beef twenty times a year and buy it at the store or in a restaurant, you are eating beef from something on the order of three hundred different cattle.
When you buy from Vermont Natural Beef, everything you get comes from one side of beef. Nothing is blended in from other animals or other sources. The grinder is cleaned between every half or side. Large-scale operators — including premium retailers — cannot do that and hold their margins.
That single fact is a big part of why people are so particular about our burger: it is a truly custom grind, from your animal only.