> Last week purchased some vacuum-packed lamb that had a manufacturer label with an expiration date a month away, but was prominently labeled to expire this week.

Are you sure this was an expiration dates, and not a "sell by" or "best before" date?

A sell-by date is the date at which the grocery store will voluntarily throw out the product—not because it has gone bad, but rather because its unprepared appearance/texture will have changed enough that people will either avoid the product on the shelf, or will complain and return the product, even though those differences disappear once the product is prepared. I'm talking here about things like "bruised" bananas, "slimy" baby carrots, raw chicken that's turned a slightly deeper shade of pink, and anything that "smells off" when taken out of the package. The grocery store can't make a profit keeping these products on the shelf past a certain point—even though they're perfectly fine and safe to eat—so it does some Business Intelligence stuff to optimize the profit-curve given (shelf-space opportunity-cost + complaint PR-cost + return-cost), and out comes a number they print on the label for when they should remove the thing to replace it with a newer one if they want to make the most money.

You might think that this makes for a lot of waste. But grocery stores are aware of this waste, and how it translates directly to lost profit opportunities, so they're usually on the hunt for ways to solve this. This is why so many groceries have in-store delis that make ready-to-eat meals: it's a way to turn products people aren't willing to buy, into products they are, by doing the preparation step themselves.

Often, also, grocery conglomerates have "up-market" and "down-market" marques they operate under. Down-market customer bases have higher tolerance for these "red-herring signs of spoilage" (probably because they've at some point tried these foods out of necessity and found out they were fine after all), so the conglomerate can take advantage of this when building a centralized logistics pipeline for its stores: when it acquires produce/dairy/meat/etc., the stuff that already has some of these signs (or will likely acquire them sooner) is sent to the down-market-branded stores, while the up-market-branded stores get the products that appear fresher and will continue to appear fresh for longer. This is a necessity—if they didn't do this, they wouldn't be able to keep the up-market stores in stock given said stores' customers' intolerance for signs of spoilage—but it conveniently allows the up-market store brand a cachet of having "the freshest" produce, allowing them to justify charging more for food from the same farms.

And, finally, some grocery chains have deals with e.g. homeless shelters, to provide them these voluntarily-expired products as ingredients for free-meals programs. Grocery stores get people to feel good with "can drives" for food banks, donating non-perishables, but perishables are in much greater demand, and it's often the stores themselves that are doing the most good there. (Why don't they talk this up for PR? Because the fact that this is "expired" food would have to come up, and the public will never bother to read and understand what I just wrote above.)