Many of us, I think, have smuggled in a Marian antiphon at the end of Communion before. Crawford Howie's chapter Small is beautiful: Schubert's smaller sacred works (in The Unknown Schubert) attempts to make a case for Schubert as a composer of plenary masses, and suggests that Salve regina and Tantum ergo (of which there are numerous settings) were commonly used for offertory and communion, respectively. Unfortunately no footnote documentation is offered: is the first part of that generally accepted as a common Viennese practice?