This is an extremely complicated situation, and I'm afraid I had a hand in it. I created the AR for Molinet, Jean, ǂd 1435-1507. ǂt Romant de la Rose moralisé, with the errant 500 reference "ǂw r ǂi Prose adaptation of: ǂa Jean, ǂc de Meun, ǂd approximately 1240-approximately 1305. ǂt Roman de la Rose."
I had posted the question of authorship of "Roman de la Rose" on this list at the time. I was then and am now of the opinion that the work should be entered (as it originally was, decades ago) under title. It is not a case of a poem "Roman de la Rose" by Guillaume de Lorris with a later continuation by Jean de Meun. Instead, the entire poem, as usually read and studied, consists of the two parts by the two separate authors. This quote is from Wikipedia, but other sources I checked agreed.
"The poem was written in two stages. The first 4058 lines, written by Guillaume de Lorris circa 1230, describe the attempts of a courtier to woo his beloved ... Around 1275, Jean de Meun composed an additional 17,724 lines." (This quote is from 2017; the passage has since been expanded but this is still the essence.)
There is not now and never has been a 400 or 500 on the author-title AR for Guillaume ... Roman de la rose to connect Jean de Meun to the poem, which is approximately 80% his work.
To read my argument from 2017, and Bob Maxwell's reply (the only one I got), which convinced me not to change from author-title to title, see these two posts:
When I constructed the second 500 for Molinet's Romant de la Rose moralisé as "Prose adaptation of: ǂa Jean, ǂc de Meun, ǂd approximately 1240-approximately 1305. ǂt Roman de la Rose," I believe my original intention was to create an author title NAR for Jean's portion, as Jean, de Meun ... Roman de la Rose" with a 400 from Jean, de Meun ... Roman de la Rose. ǂp Lines 4,059-21,782," but then I hesitated, because it's not really a part, it is the whole of Jean's contribution to the poem. I was still mulling over the possibility of changing the author-title for Roman ... back to a straight title (Bob Maxwell said he would have no objection to that), but I hesitated mainly because of all the 240's under Guillaume de Lorris out in the world that aren't controlled and that wouldn't get changed automatically; all editions of the Roman would have to be recataloged, with the main entry changed to the title and Guillaume moved to an added entry.
I gave up before I had resolved it, and just added the NAR as I had composed it originally. So that is my fault.
Perhaps it would be best to go ahead and create the name-title AR for "Jean, de Meun ... ǂt Roman de la Rose," with a 500 to Guillaume de Lorris ... ǂt Roman de la Rose, and notes explaining the situation? (And a similar 500 on the Guillaume de Lorris ... Roman record?) Future editions of the entire Roman would then be cataloged as compilations of the two parts and entered under whatever title is in the work, with the two author-title added entries.
That is the best I can come up with now, three years removed from deeper contemplation of the issues involved, at least.
Rare Materials Cataloger
Miriam and Ira D. Wallach Division of Art, Prints, and Photographs
The New York Public Library
Stephen A. Schwarzman Building
476 Fifth Avenue, Rm. 313, New York, NY 10018
My opinions, not NYPL's