This would explain why different documents within Wells-Gardner itself disagree on its size. Whoever came up with the model number was obviously used to arcade specs, and wrote it as an 18", but since it is technically a PC monitor, it's official spec sheet shows it as a 19".
This does bring up an interesting point, though! I was about to buy a Happs 19" bezel for it, but since that bezel would be designed for an arcade 19" and not a PC 19", it would be too big for this monitor, wouldn't it?
--Chris