Ok to number 3 from the German wikipedia so i have an source. The german wikipedia itself has as source The "german Museum of History in berlin" that should be relieable enought on this. What did i want to say? Ah yes!:
"Qualitativ hochwertige Plattenpanzer wurden im 15. Jahrhundert gegen Armbrustbolzen, im 16. und 17. Jahrhundert gegen
Arkebusen- und
Pistolenschüsse getestet. Wenn der Bolzen bzw. die Kugel vom Brustpanzer abprallte, wurde dieser mit dem Beschaustempel der entsprechenden Plattnerzunft versehen [...] Nur wenige Rüstungen konnten erfolgreich gegen
Musketenschüsse getestet werden"
Translation (a bit rought thought):
"High Quality Platemail was tested in the 15 Century against Crossbowbolts, in the 16th and 17 Century against Arkebuse and Pistol shots. If the the Platemail deflected the Bullit/Bolt it got the quality seal from the producing Plating guild [...] Only a few Armors were teted succesfully against Muskets."
You see Platemail was efective aigainst crossbows and if you still dont believe me here an Picture of an platemeil wich got tested against an crossbow:
As sidenote: Your weapon needs an certain force and crossection if you want to break throught thick plating. An Platebreaker ("Panzerbrecher"/"Panzerstecher"/"Miséricorde") the ancestor of the latter Stillet had an triangular or sometime rectangular crossection and to get through think plates you had to use both hands.
This weapons were wonderfull against normal Chainmail to cause they were pionty as an needle and could by this lodge into one ring and break it from the inside while being pressed deeper in the flesh of an victim. They were poor cutting weapons on the other hand which was an mayor problemm against unarmored troops like light infantary.