HiWhy do some of the aircrafts turns-up or shows under the "UNSPECIFICS" of MSFS Aircraft Menu?Thanks

You have to understand how the aircraft are assaigned there 'order' in FS.(From the default 747-400 aircraft.cfg)ui_manufacturer=Boeing <-- This line tells the sim who made the plane. Without this line, it is 'unspecified'ui_type=747-400 <-- This is the model number. I believe nothing in this field also puts this plane in the unspecified column, but I could be wrong.ui_variation=Global Freightways <-- This is the variation of the plane. This is the final level of the 3 clicks you have to do when you choose an airplane.I hope that makes it clearer.