User blog comment:B214/Volume 17 spoilers./@comment-121.54.54.40-20140515155159/@comment-16281343-20140518064031

Well, even if Rias and Issei aren't engaged in the eyes of the normal public, they are in the eyes of the higher ups and the nobles since even Seekvaira knows that Issei will be Sirzechs' brother-in-law even before Issei confessed to Rias.