[Tink]

Here our meat is processed and cut by one of 2 local meat markets. It's very good quality, fresh, and I've never heard anyone complain about it. The same 2 markets sell to most of the local groceries and have a retail sales area of their own. None of my meat is stamped.
My son used to work at one of them, and he said the business is USDA inspected, but no one is there on a daily basis checking things out.

My husband was a security guard at a much larger meat processing plant many years ago. He said that in the larger plants they do have full time USDA inspectors who supervise and check quality and storage and so on daily. So it sounds like the size of the business determines how often the place is inspected and if it's not stamped, it likely comes from a smaller plant.