The 19 millionth Vespa unit was an anniversary edition GTS 300. (Piaggio Group/)Vespa hit its 75th anniversary earlier this year and also celebrates 19 million scooters produced with a special 75th series that includes limited-edition versions of the Primavera and GTS. The actual 19 millionth unit was a GTS 300 produced at the brand’s Pontedera plant, where the whole story…