That's a fascinating item, thank you for the pointer. Of course it is not about ancient Christian texts.
Putting aside whether modern standards are fairly applied to ancient intellectual property concerns, the modern standard for plagiarism is, if a dictionary is to be believed,
The practice of taking someone else's work or ideas and passing them off as one's own.
I believe that that definition fairly reflects actual usage. An element of the the offence, then, is to claim ("passing off") some work or ideas as being somebody
's. Since Mark
are unsigned works, this element of the offence is missing. Luke
is both unsigned and famously acknowledges antecedents, claiming credit only for the "orderliness" of its author's work, which so far as we can tell appears warranted. Thus, all elements of the offence are missing from Luke
. Finally, John
is unsigned, and does not closely resemble any extant antecedent.
Simple failure to attribute to a specific source is not an element of plagiarism. It is a fault in scholarly works, but it is a separate concern from false attribution. Also, it is not plagiarism when later readers impute authorship unreliably. Matthew
copies a lot of Mark
, but that isn't plagirism unless there was a "Matthew," different from a "Mark," who personally and affirmatively claimed originality. We have no hard evidence that either such individual person existed. John
is an esepcially odd "later reader misattribution," since an acknowledgment of a source in the text has often been construed as an authorship claim for the whole work.