Fourteenth Century Verse & Prose, Sisam's collection, was a groundbreaker in its day, anything but interchangeable with others. As originally published in 1921 (Oxford, at the Clarendon Press), the 300-page "Fourteenth Century Verse and Prose" had an excellent introduction, interesting texts with informative headnotes, detailed technical endnotes, and an appendix on "The English Language in the Fourteenth Century." However, it lacked a glossary.
This appeared separately the following year, as "A Middle English Vocabulary," about 170 double-column pages (no numbering), compiled by one of Sisam's colleagues, none other than the young J.R.R. Tolkien.