I know that Fiat Punto Grande, Vauxhall Corsa, Alfa Mito, Lancia Ypsilon (AKA Chrysler Ypsilon) are all cars from the same platform.
Fiat 500 and Ford Ka are also from the same platform.
But today I spotted a Fiat Punto Evo parked next to a new Ford Fiesta, the resememblence was uncanny. Change the front grille, and the Fiat Punto Evo transforms into a Ford Fiesta and visa versa. Is this a new platform from the old Punto? Otherwise you would have Vauxhall = Ford, which can't be true?