For example Rimmers advertise 3 grades of parts: LR or MGRover factory"parts, Original Equipment Manufacturer parts, and Aftermarket parts. Genuine LR parts are labelled LR no matter where they were made, OEM parts were made by the same manufacturer-wherever, and aftermarket aren't necessarily made in the same country as the other two, likely somewhere cheap.
I do understand your point. A couple of years ago I bought an MG part from Rimmers which came in an MGRover bag, marked Made in England and dated long after MGRover ceased to exist. When the bag was opened the part had a Chinese label. I can't blame Rimmers for this, they can hardly be expected to open every package to inspect the part before it is sold, but somewhere along the line someone either neglected to adjust the labelling or deliberately left the Made in England in place.