Excess production, seconds or rejects from the factory possibly. I've seen a lot of PRL like that, always good quality, sometimes tags and labels removed or defaced though, which is what can happen with seconds. Bought a job lot of RL polo shirts like that last summer in Shenzhen.
The contractor that makes them for RL are supposed to destroy anything that fails to meet specs, but they don't usually. So they might end up on Ebay or whatever. Sometimes they'll go on making more than what the client ordered and just sell them out the back door.