It appears as though Savage doesn't stamp barrels until they are staged for assembly. When I bought a 6.5 Creedmoor barrel from them in 2014, it came without any roll stamps, just threaded and chambered. Same/same for the 22-250, 7mm-08, and 375 99 barrels that GPC used to sell. The 24" barrel could easily be explained as a finished, or partially finished, 99EG or 99R barrel.
However, since the rifle in question is a non-cataloged configuration and there isn't even a factory letter to validate what it actually is, any story a seller or buyer want to concoct is as good as any other. The better the story, the higher the price.
