I agree, me saying it doesn't make it so, the obvious flaws (which your comments are highlighting) make it so.

"Your logic basically invalidates every survey of any kind, because there's ALWAYS going to be differences between what was sampled and what wasn't."

Not including corporate-owned multi-sites is not mere "sampling" variance that would be included in a margin of error. It is exclusion of an entire category of data. If they had included statistically valid estimates of how many jobs were added or lost at those businesses, their study might be credible. Instead, it is bunk.