I don't think the motherboard has the serial number (it might...), but if you're comfortable opening the thing up, there's a big rectangular chip right next to the buttons, and it should have a white sticker on it. And then there's a smaller, square-ish, socketed chip to the right of that somewhere, which should also have a sticker on it. If you can photograph these, we might be able to figure out how old your Evolver is.
Also: Is the big rectangular chip with the sticker on it socketed or soldered directly to the circuit board? My memory is a bit hazy, but I think that these are socketed in early Evolvers, and directly soldered later on. They could be replaced, as I recall, in older Evolvers. Not with the newest version, but with a newer version. Anyway, pictures would be helpful.