Hartge made that designation sometime past the E28 on the 5 series. On that car it would have been a package- wheels, suspension, body, a little interior ( probably recaros) and the engine was tuned up.
It would have once had the valve cover and been 247+- hp. Who knows now? Interesting selling point though if it can be confrmed.
I think Hartge got their manufacturing designation in '86.