I believe the original question is most likely "029 dressed up to look like an 039" (038 is an entirely different saw). Very easy to do as both saws look physically the same (just change the top tag on the units prior to decomp valve) and very hard to detect without looking at model specific details like the diameter of the bore.
Sometimes the current owner (or ebay reseller, or pawn shop) will make an honest mistake - he may have bought it as an 039 but the prior owner has broken the handle and changed it for one from an 029. Same in reverse - I've seen more than one '029" that was actually an 039 with 029 handle/tag. I got caught when buying an 075 that turned out to be an 051. I've even bought a few things on ebay that were labled wrong, but I knew that and the seller didn't.....