When I was looking at Corvettes I went to a dealer that specialized in them. One particular car caught my eye and I asked if it was a Numbers Matching car, to which they responded "Yes." We talked a little longer and I told them I was impressed by car X because it had it's original engine, to which the dealer responded, "I don't know if the engine is original, only that it is Numbers Matching." Long story short, it was obvious to me they very carefully chose their words for this particular car. I suspect engine restamping is much more common then you might think.