I suppose this could be done, but what's the difference in the end? I like SY II instead because when you click on it, it only shows SY II and doesn't include SY. The difference between the two was more than just minor, there were big changes (more changes than SX -> SY for example). SY II was essentially a new model code, except for some reason Ford decided not to give it a new model code.

It's not like SZ and SZ series II, where it was a minor update.

In short, SY II was a big upgrade, worthy of having its own unique code separate from SY.