In his 2003 master’s thesis at Laval University, under the direction of Paul-Hubert Poirier, Steve Johnston discusses the text of 3 Cor provided by Willy Rordorf, at the end of his article, “Héresie et orthodoxie selon la Correspondance apocryphe entre les Corinthiens et l’apôtre Paul”, in Orthodoxie et hérésie dans l’Eglise ancienne, Cahiers de la Revue de Théologie et de Philosophie 17:60-63.
Johnston writes as follows (p. 161, n. 45):
The explanation, if I’m not mistaken, is that the text that Rordorf provides in his 1993 article is a preview of his forthcoming edition of the Acts of Paul which will appear in the CChrSA (Brepols). Thus, Rordorf will provide an edition of the 3 Cor only as it was integrated into the Acts of Paul. Bodmer X provides what is believed to be the independent Greek text of the 3 Cor which evidently predated the Acts of Paul. Every text which stems from the Acts of Paul, starting with the Heidelberg Coptic Papyrus, has the words “other apostles”.
By the way, if Steve Johnston himself happens upon this blog post, it would be great for him to contact me.