There’s nothing special about titles of works: as with anything for which there are multiple names, you choose the name that best suits your purpose and your audience. The same chemical substance might be called “table salt” when writing for an audience of cooks but “sodium chloride” when writing for an audience of chemists.
Taking Malory as an example, if you want to refer to the manuscript, then you can refer to it
by its shelfmark: British Library Add MS 59678;
by its common name: the Winchester manuscript, but only if the context is clear, as there is another “Winchester manuscript” of the Anglo-Saxon Chronicle (Parker Library MS 173);
by its abbreviation: W, but again the content needs to be clear, as many other works have a manuscript W;
or you might make up your own name for it!
Traditionally it is referred to as ‘W’ for ‘Winchester’, but since it is now known as BL Add MS 59678 I have called it in the present study ‘the Malory manuscript’.
Lotte Hellinga (2014). ‘William Caxton and the Malory Manuscript’. In Texts in Transit: Manuscript to Proof and Print in the Fifteenth Century, p. 410. Leiden: Brill.
If you want to refer to a specific printed edition, then you use the title of that edition:
- the 1485 Caxton edition has the title The Byrth, Lyf, and Actes of Kyng Arthur; of his Noble Knyghtes of the Rounde Table, theyr merveyllous enquestes and aduentures, Thachyeuyng of the Sanc Greal; and in the end Le Morte Darthur, with the dolorous deth and departying out of thys worlde of them al which everyone understandably abbreviates to Le Morte Darthur;†
- the 1906 J. M. Dent edition, Le Morte d’Arthur, is typical of modern-spelling editions in regularizing the spelling of the title.
If you are referring to the work generally, and not to a particular edition, you can choose based on your purpose and audience. If you’re doing textual criticism for an audience of scholars then you’ll want to stick to original spelling, preferring the title Le Morte Darthur and the text beginning:
Hit befel in the dayes of Vther pendragon when he was kynge of all Englond and ſo regned that there was a myʒty duke in Cornewaill that helde warre ageynſt hym long tyme
but if you’re writing for a general audience then you’ll want to modernize the spelling to make it easier to read, preferring the title Le Morte d’Arthur and the text beginning:
It befell in the days of Uther Pendragon, when he was king of all England, and so reigned, that there was a mighty duke in Cornwall that held war against him long time.
Note that the title The Death of Arthur is generally not used for Malory’s text, but instead for the alliterative Morte Arthure, a Middle English poem; and the title The Death of King Arthur is used for La Mort le Roi Artu, an Old French prose romance.
† See this 1817 reprint. I was unable to find a scan of the original title page, so I am not sure whether the capitalization is original. There are only two surviving copies of the Caxton edition: the one at John Rylands University Library in Manchester is missing the first pages, and the one at the Morgan Library in New York is not digitized.