kashering glass

Question

Under the Jewish laws of Kashering section of the website, you state “Glass, plastic, glazed china, glazed dishes, Corelle, Pyrex, Corningware, or glazed earthenware does not need any Koshering for Passover, since they do not retain any flavor.” Do they not need any koshering for Passover, or do they not need any koshering in general. For example; if it is used to cook milk and meat within the same 24 hour period, or if it is used to cook non-kosher food. Thanks