If you compare the keyboard of the Tandy 3 with the FCC evaluation unit pictured above, it appears as if the Tandy 3 case was probably used to house what was then the new TRS 80 Model 4. The name "Tandy 3" is a late model TRS 80 Model III, perhaps intended for the schools/education market
It is very possible that Roy Soltoff stuck the "TRS 80 Model 4" plate to the computer from some other system at the same time he put the 128K stick on the keyboard. These very possibly were not present when submitted to the FCC for testing. No way to know.
The FCC warning label is the only marking on the bottom of the unit.