That's weird, those transistors are very common and cheap, so I see no reason why one would take the effort to re-marking (counterfeiting) them, unless someone was trying to literally sell garbage (parts that fail all tests end up in the dumpster bin of the factory. Depending on the wealth of the dumpster diver, some might try to sell out-of-spec parts.
Maybe it's a mistake in the datasheet
(well, once I found a transistor pinout mistake in a datasheet, but that was in a local paper-printed catalog, way before the PDF datasheet era)
My best guess is that you bought some other parts that were labeled by mistake as 2N3904 by the factory, so that particular batch was discarded, and the dumpster-diver somehow managed to sell them as 2N3904, even if they are something else.