There's a lot of contradictions in GK
fluff, such as Nemesis Force weapons being only attuned to one GK
... oh wait, OM Inquisitors can all have one!
Nemesis Force weapons can only be used by the single Psyker it's attuned to ... except for that relic, anyone can use that!
Grey Knights are so secretive no one outside of a select few know about them ... except for every Chapter Master, all the High Lords, every Imperial Guard Lord Commander, all every mom in the Imperium that just wants their little brat to eat their mush and go to bed!
“And they had breastplates, as it were breastplates of iron; and the sound of their wings was as the sound of chariots of many horses running to battle.”
- Revelations 9:9