I just don't buy that, mainly because the results of ignorance is so deadly. According to Bob the last time there was a rampage by a Loop was in the 1600s, stuff like that isn't kept under wraps unless the family is well aware of it. Heck Finn himself couldn't functioned in the military of all places unless he knew the ins and outs of his curse.
I think we should presume the MacFinn lineage was in possession of the major Circle since that 1600's date.
If they were able to keep the circle, it seems to follow they likely have continuous family lore since that date, too.
That "outbreak" (in the 1600's) might have represented a
discontinuity in Circle-possession & family-lore. The main family line may have died out, and they were unclear who would inherit. Then they had to wait to find out who wolfed-out, and maybe it was a very distant relationship. Eventually the horror story reached the family-in-the-know, and they rushed circle & family-records to the site...
(all of which presumes the 1600's Loup (as mentioned by Bob) was a Loup of the MacFinn line, and not some other Loup; maybe the MacFinn's were safely under control through this time ... But I presume Jim wouldn't have written Bob's line to be irrelevant, so...)