Manufacturer's plates are used on road test and promo cars. Into the early 70's, the manufacturers used to produce a number of cars each model year and introduce the new model (car was kept under wraps until the big unveiling) with these cars. It was a big event to see the new cars. Some were used primarily for test track sessions by magazine reporters, some were show cars, some were road test cars. Most of these cars, other than those that were pre-production test mules, were eventually sold to customers or employees.

They were not used by service reps or sales reps here in Michigan. The manufacturer plates are still in use here, I see cars in body mask driving around quite often on road evaluations. The plates are also used by the engineering teams for long-term testing.