Ah, but like your M70/87/15, they were issued to Italianrear echelon troops during WW1. The Italians also issued the Vitali magazine fed M70/87 as well. They also sent a number of Vetterlis - single shot and Vetterli-Vitali - in the original caliber as aid to Imperial Russian
forces for use on the Eastern Front. So all of the versions of the Vetterli were WW1 issued.
But of course, you are right, there has to be a cut off somewhere or
For an excellent, short but detailed article by one of todays top collectors of WW1 firearms, equipment and uniforms see John Sheehan's article from his series of articles for Guns Magazine at:
Web Blast: Italian Shoulder Arms Of WWII | Guns Magazine
John's collection and knowledge about WW1 details are to die for.