i think there could be some criteria that we can use to judge if an argument has a claim for "narutoverse historicity."

(please do add some criteria that you think is beneficial.)

Some criteria for determining
"historicity" of data
in Narutoverse

1) first, the data should be clearly stated/indicated in the manga. (the event, character, place, time is written/documented/stated in the manga=history)

2) any detail that is not clearly stated should be established by reason/logic or logically sound argumentation (e.g. the deductive/inductive method) and should fulfill some of these other criteria:

a) the criterion of coherence: "new data" can be reasonably established as facts if they necessarily conform to already established historical facts (in the manga)

i) by a matter of relation (again could be the relation of the whole and its parts; or of personal relations) or
ii) by a matter of necessity (the relation of cause/s and effect/s)

b) the criterion of anime support: the claim for historicity is strengthened dramatically if the anime confirms the detail of the incident, character, place, time, etc. there are indeed a lot of dimensions of reality that the anime provides which is not clear or available in the manga

c) authentic "spoiler" interviews from the author himself

d) consensus of translators as to the correct meaning of a japanese text/dialogue that is causing confusion/misunderstanding

e) adherence to rules or techniques to manga story-telling/ or narrative plot development

DUBIOUS Criteria:

1) supposed parallelism with other manga (e.g. Dragon Ball GT)
2) the similarities with japanese myth or legends (e.g. Tengu legend)
3) naruto movies and games
4) reader poll outcomes
5) "supernatural" talents possessed by characters, esp if it used to claim that "nothing is impossible and everything/anything is possible" in the narutoverse
6) relations of a private nature with the author Kishimoto

note: this is a preliminary draft, please do add/correct/clarify if you see we can develop these criteria