The "parking garage can hold another level" is an urban legend that is propagated on this message board. Universal would not build two massive garages in 1998 and leave an option to add ONE level on ONE garage. That's a negligible amount of extra capacity, and the expense of adding a level in the future would be 20 times the cost of building it during the initial construction. Please put this one to rest
Also, regarding "master plans". It's important to remember that there is no secret master plan with details of expansion over the next 10 years. In this industry, things move swiftly and are only planned a couple years out, max. When MIB was constructed, Universal went from "no idea on paper" to an open ride in just 28 months. So although sometimes you will see "master plan" maps for expansion, they are just created so the city has some sort of expectation of future land use, and to keep investors excited, etc. But ultimately, everything changes up until the very last second and they are constantly updated. Crazy, but true!