To use an old proverb, "The proof is in the pudding." This is really a shortened version of the even older proverb, "The proof of the pudding is in the eating." What both mean is that the true value or quality of something can only be judged when it is put to use. When we use the phrase, we mean something like "the results are what count."
When I think of this in terms of the historical Jesus, or my own work on the Gospel of Thomas, what this means is that a methodology has done its job well if the results make sense given everything else we know about Second Temple religiosity and the formation of early Christianity. For me, this means that if Jesus doesn't look Jewish, then there is probably a problem with the method, and it needs to be adjusted.
In terms of the Gospel of Thomas, if my method yields information about the text and its theology that is in accord with what we can know about other early Christian texts and their theologies, then my method has done a satisfactory job.
It is like my algebra teacher in high school used to tell us. If your answer looks off, you probably made a mistake.