Which short stories are falsely attributed to Guy de Maupassant, and why?

Question

Thanks to @GarethRees's sleuthing and editing, I just learned that several French short stories found in the Project Gutenberg version of the "Entire Original Maupassant Short Stories" are in fact not by Maupassant at all, but by other authors and falsely attributed to him. These include "The Lancer's Wife" by Richepin and "The Confession" by Maizeroy, and I don't know how many others. So my question now is threefold:

1. Exactly which short stories are falsely attributed to Guy de Maupassant in collections of his complete works?
2. Where did these misattributions begin? Can we blame Walter Dunne's collection of English translations, or does the origin go back further? Have French-language collections ever contained stories misattributed to Maupassant?
3. Why did this happen? Was it just poor research on the part of Walter Dunne or whoever, or was there any ulterior motive for over-promoting Maupassant?

Answer 1

The ‘which’ and ‘where’ parts of the question were answered by Maupassant’s biographer Francis Steegmuller:

A smart American publisher and bookseller named M. Walter Dunne, whose specialty was large and showily produced “sets,” felt that the time had come to confront the American public with all of Maupassant; and he issued [starting in 1903], in seventeen volumes, the first large-scale collection of the stories, novels, travel-writings and verse in English. […]

But the most remarkable feature of the Dunne collection is its contents: for in it are included no less than sixty-five stories which are not the work of Maupassant.

None of these sixty-five stories has ever been included in any French edition of Maupassant’s works; I have been able to identify four as tales from the collected works of one of Maupassant’s fellow-journalists, René Maizeroy; the authorship of the remainder is unknown; but almost without exception internal evidence shows them to be non-Maupassantian. Falsity is particualrly obvious in those dealing with Central and Eastern European life, especially Vienna and Budapest society, territory never explored by Maupassant, and here described in a very non-Maupassant style. Almost all of the sixty-five give the impression of having been trash in their original language or languages, whatever it or they may have been.

The Dunne collection was followed, during subsequent years, by many smaller, less elaborate Maupassant collections for smaller purses, and although Dunne's collection was copyright it seems to have been without real protection, for in the later collections various of the fake stories first published by Dunne continued to appear and reappear.

_{Francis Steegmuller (1949). Maupassant: A Lion in the Path, pp. 355–357. New York: Grosset & Dunlap.}

The following list gives, for each of the fake Maupassant stories, its English title (or titles; some stories were reprinted under different titles), its true author, its original title, and the collection in which it appeared. The list was compiled by Kazuhiko Adachi (足立和彦) and contains the 65 fake stories found by Steegmuller, plus one more (‘Mad’) found by Onishi Tadao (大西忠雄). The stories are by René Maizeroy (28), Jean Richepin (20), and Leopold von Sacher-Masoch (18).

English title(s)	True author	Original title	Collection
‘The Accent’	Maizeroy	‘L’Accent’	En folie
‘An Adventure’	Richepin	‘Une Aventure’	Cauchemars
‘The Artist’	Richepin	‘Artiste’	Truandailles
‘Babette’	Richepin	‘Ch’tiote’	Truandailles
‘The Bandmaster’s Sister’	Maizeroy	‘La Sœur du chef’	Coups de cœur
‘The Carnival of Love’	Sacher-Masoch	‘Karnevale der Liebe’	Die Messalinen Wiens
‘The Carter’s Wench’	Maizeroy	‘La Fille aux rouliers’	La Fête
‘Caught’	Sacher-Masoch	‘Gefangen’	Die Messalinen Wiens
‘The Clown’	Richepin	‘Pouillards’	Truandailles
‘The Confession’	Maizeroy	‘Le Confession’	En folie
‘Countess Satan’	Richepin	‘Comtesse Satan’	Cauchemars
‘The Debt’	Richepin	‘La Dette’	Truandailles
‘A Deer Park in the Provinces’	Sacher-Masoch	‘Ein Hitschpark in der Provinz’	Die Messalinen Wiens
‘Delila’	Sacher-Masoch	‘Delila’	Soziale Schattenbilder
‘False Alarm’	Maizeroy	‘Fausse Alerte’	Coups de cœur
‘A Fashionable Woman’	Sacher-Masoch	‘Die Frau nach der Mode’	Die Messalinen Wiens
‘Ghosts’	Sacher-Masoch	‘Gepenster der Kirche’	Soziale Schattenbilder
‘A Good Match’	Sacher-Masoch	‘Eine gute Partie’	Die Messalinen Wiens
‘Happiness’	Maizeroy	‘Le Bonheur’	Coups de cœur
‘The Hermaphrodite’	Maizeroy	‘L’Hermaphrodite’	La Fête
‘An Honest Ideal’	Sacher-Masoch	‘Ein eheliches Ideal’	Falscher Hermelin
‘The Ill-Omened Groom’	Sacher-Masoch	‘Der verhängnisvolle Jockey’	Soziale Schattenbilder
‘In Flagrante Delictu’ ‘Caught in the Very Act’	Maizeroy	‘Le Flagrant Délit’	Coups de cœur
‘In His Sweetheart’s Livery’	Sacher-Masoch	‘In der Livree der Geliebten’	Falscher Hermelin
‘In Various Roles’ ‘An Exotic Prince’	Sacher-Masoch	‘Ein exotischer Prinz’	Soziale Schattenbilder
‘The Jennet’	Maizeroy	‘Le Genêt’	Coups de cœur
‘Jeroboam’	Richepin	‘Jéroboam’	Cauchemars
‘Julot’s Opinion’	Richepin	‘L’Opinion de Julot’	Truandailles
‘The Lancer’s Wife’	Richepin	‘La Uhlane’	Les morts bizarres
‘The Last Step’	Maizeroy	‘Le Dernier Pas’	La Fête
‘Lilie Lala’	Maizeroy	‘Lilie Lala’	Coups de cœur
‘La Morillonne’	Richepin	‘La Morillonne’	Cauchemars
‘Lost’ / ‘Crash’	Sacher-Masoch	‘Krach’	Die Messalinen Wiens
‘Mad’	Maizeroy	‘En folie’	En folie
‘Mademoiselle’	Richepin	‘Mademoiselle’	Cauchemars
‘Mamma Stirling’	Maizeroy	‘Maman Sterling’	Coups de cœur
‘The Man with the Blue Eyes’	Richepin	‘L’Homme aux yeux pâles’	Cauchemars
‘The Man with the Dogs’	Richepin	‘Cht’Heumme-aux-quiens’	Truandailles
‘Margot’s Tapers’	Maizeroy	‘Les Cierges de Margot’	Le mal d’aimer
‘The Marquis’	Richepin	‘Le Marquis’	Truandailles
‘A Misalliance’	Sacher-Masoch	‘Eine Mesalliance’	Soziale Schattenbilder
‘The Mountebanks’	Maizeroy	‘Les Monteflores’	Celles qu’on aime
‘The New Sensation’	Maizeroy	‘Le Frisson nouveau’	La Fête
‘A Night in Whitechapel’	Richepin	‘Ivres-morts’	Cauchemars
‘The Odalisque of Senichou’	Sacher-Masoch	‘Eine Smichower Odaliske’	Soziale Schattenbilder
‘The Old Maid’	Maizeroy	‘Vielle fille’	Coups de cœur
‘Profitable Business’	Richepin	‘Une Bonne Affaire’	Cauchemars
‘The Real One and the Other’	Maizeroy	‘La Vraie et L’Autre’	La Fête
‘The Relics’	Maizeroy	‘Les Reliques’	Coups de cœur
‘A Rupture’	Maizeroy	‘Rupture’	La Fête
‘The Sequel to a Divorce’	Maizeroy	‘Suite de divorce’	Coups de cœur
‘Stable Perfume’ ‘On Perfumes’	Sacher-Masoch	‘Stall-Parfum’	Die Messalinen Wiens
‘Sympathy’	Richepin	‘Correspondances’	Cauchemars
‘The Thief’	Maizeroy	‘Le Voleur’	La Fête
‘Ugly’	Richepin	‘Laid’	Truandailles
‘Under the Yoke’	Maizeroy	‘Sous le joug’	Sur l’amour et sur le baiser
‘An Unfortunate Likeness’	Maizeroy	‘Le Mauvais Mirage’	La Fête
‘The Upstart’	Maizeroy	‘Parvenu’	La Fête
‘A Useful House’	Maizeroy	‘L’Hôtel à tout faire’	La Fête
‘The Venus of Braniza’	Sacher-Masoch	‘Die Venus von Braniza’	Neue Judengeschichten
‘The Viaticum’	Maizeroy	‘Le Viatique’	En folie
‘Violated’	Richepin	‘Violé’	Cauchemars
‘Virtue in the Ballet’	Sacher-Masoch	‘Die Tugen beim Ballett’	Falscher Hermelin
‘Virtue’ / ‘Kind Girls’	Richepin	‘Bonnes filles’	Truandailles
‘The White Lady’	Sacher-Masoch	‘Die weiße Frau’	Die Messalinen Wiens
‘Wife and Mistress’	Maizeroy	‘Naufrage’	En folie

To answer the ‘why’ of the question is probably impossible now, but it is easy to imagine plausible scenarios. Perhaps the publisher had employed a translator in Paris to go to the archives of Gil Blas, La Lanterne and so on, dig out old stories by Maupassant, and submit English translations, at so many cents a word. An unscrupulous translator might have found it tempting to eke out a little extra cash by passing off some stories by other authors. Or, more likely, the publisher deliberately included the more risqué and sensational stories of Maizeroy, Richepin and Sacher-Masoch, in order to increase the appeal of the collection.