Others such as Corsa and Vectra were redirected to Opel as that was where the names were originally used, or where the Vauxhall version (e.g. Nova) would only be part of the Opel model article. Astra was originally a Vauxhall name so the situation would be reversed (and Vauxhall Astra shouldn't be a disambiguation page, as it isn't about unrelated uses of a name).     