I am currently reading From the Mandylion of Edessa to the Shroud of Turin by Andrea Nicolotti, which provides a far more detailed description of the history and development of the Abgar-Jesus tradition.
This passage seems relevant:
To summarize the arguments thus far: originally, the Edessean legend concerned an epistolary correspondence between Jesus and King Abgar. The story of the image was created as an appendix to that legend, but it gradually superseded it. There are no records of the existence of an image of Christ in Edessa before the fifth century. The oldest source that mentions it refers to a handmade image, painted with colors (Doctrine of Addai). The first news of an acheiropoieton dates to the sixth century (Acts of Mar Mari and Evagrius). It is more likely that the appearance of this acheiropoieton took place after the siege of Chosroes in 544, not before. There are traditions that, even after the sixth century, ignore the existence of any kind of Edessean image, or know it only as a painting and ignore the transformation into an acheiropoieton, which took place elsewhere.
Nicolotti also discusses the quoted Saroug passage, making the following points:
- The authenticity of this passage is disputed:
Han Drijvers believes that this is clearly a “later interpolation.”46 This would be confirmed because elsewhere, the same Jacob of Sarug, when speaking about Edessa and the story of Abgar, never mentions the image. Andrew Palmer, instead, deems the text credible and states that Drijvers’ argument is “circular.” In his opinion, the ease with which the author speaks suggests that readers had a perfect knowledge of the existence of an image of Christ in Edessa, which is why there was no need to dwell on its features.
- The description given is vague and generic, and far from contemporaneous:
But what features would these be? Since in the Life of Daniel there is mention of a generic image of Christ without any specifics, it is not possible to know whether the author (or the interpolator) had in mind the normal painting of Ananias or the miraculous acheiropoieton. In addition, although the visit of Daniel is ascribed to around the year 410, here we are dealing with a text written almost a century afterwards. One cannot assume that Jacob of Sarug was able to report with accuracy anything that happened forty years before his birth. Even if the authenticity of this passage was confirmed, a substantial modification of what is already known would not follow automatically: in the second half of the fifth century it was well known that an image of Christ was kept in Edessa.
Addendum:
I would also note that Jacob of Sarug’s authorship may be in doubt. Nicolotti only lists the work as being “attributed” to him. In a footnote he states:
Andrew Palmer plans to edit this work (“The Logos of the Mandylion,” cit., p. 186, note 218). Summary of the work in F. Nau, “Hagiographie syriaque,” Revue de l’Orient chrétien 15 (1910), pp. 60–62, based on ms. 235 of the National Library of Paris. Mario Moroni claims that this Parisian manuscript – of which he provides the photograph of a detail (f. 165a, col. 2) – would date from the fifth century (“L’icona di Cristo nelle monete bizantine,” in L. Coppini – F. Cavazzuti [eds.], Le icone di Cristo e la Sindone, Cinisello Balsamo, San Paolo, 2000, p. 126); in reality, the manuscript dates from the thirteenth century (cf. Catalogues des manuscrits syriaques et sabéens [mandaïtes] de la Bibliothèque Nationale, Paris, Imprimerie nationale, 1874, p. 187).
Further addendum:
I could find no statements explicitly casting doubt on this attribution, but it appears that (i) this attribution may of a very late date (apparently early 20th century), and (ii) this work appears to be well outside Jacob’s main body of work (homilies rather than histories). This lack of explicit discussion may be due to the fact that the “Life of Daniel of Galaš” appears to be unpublished, and thus not widely discussed.