The term "מצה שמורה", means "watched matzah". AFAIK, in making "shmurah matzot" The wheat is being watched, not the matzah, itself. Perhaps, from the time it comes out of the oven until it's packaged, it's watched, but, then again, so are "non shmurah" matzot, and I don't think that's what the term applies to, anyway.
So why not call it מצה מתבואה שמורה or something similar.
Note I used the term תבואה because nowadays, matzot are also commonly made from oats and spelt, and not just wheat.