score:5
Based in part on links posted in comment by @MCW:
The name André Du Nay appears on the cover of this book: Transylvania and the Rumanians , along another two other names: Alain du Nay and Arpad Kozstin.
But this is the same book as the one here, called The Daco-Roman Legend. The website index page displays a similar name to that of the initial publishing house ("Corvinus"), and seems to promote, at least up to a point, a Hungarian patriotic and nationalist agenda, and some far-right topics like "decline of Europe" - although many links there lead nowhere.
Amazon also lists here this longer title: Transylvania and the Rumanians: Transylvania - fiction and reality : the Daco-Roman legend, by the same three authors. -
Alain du Nay seems to be the "main author" of that book - as it appears alone here
Arpad Kozstin appears here, online as the author of the The Daco-Roman Legend.
There seems to be another book under the name Alain du Nay, in Romanian: Români și maghiari în vârtejul istoriei. ("Romanians and Hungarians in the Vortex of History"), linked here and downloadable as pdf.
The preface by the linguist Adam Makkai seems to have nothing to do with the topic of the book: it is a small article (or pages of a book) on American English, without the slightest connection with the book itself, which is about Romanian history and old history of Romanian language. All that is very dubious.
As said (in Romanian) at that link of Wikipedia discussion page:
"Alain DU NAY does not exist. DU NAY is a pseudonym (from Danube, of the Danube) used for the publication of several "true history" books, for the "education" of Transylvanian Romanians" ---and of the general public, one could add.
That might very well be an accurate assessment of this case, and a good answer for the above question.
Using a series of pseudonyms, this seems to be a semi-amateurish cultural initiative of vulgarization of the nationalist or "official" Hungarian historiography position on Transylvania against the Romanian one (nationalistic as that may be).
The scientific value of these publications is dubious. (Even potentially useful or interesting information - like that on the connection between Romanian and Albanian languages and its historical context - is not treated objectively, but uncritically instrumentalized for the sake of a cultural militancy of sorts.)