RVDT:
Ok, I understand a bit better now what you were referring to.
I'm not familiar with the specific model types you mentioned, but all the servo connections, PC links, T/R push-pull tubes etc. that I've worked on have had a self locking nut (not always easy to spot) and a cotter pin for the required redundancy. I'm just surprised that the models you mentioned apparently don't have the 2 x locking devices.
One other quick point, however:
(a) Each removable (my italics) bolt, screw, nut, pin, or other fastener whose loss could jeopardize the safe operation of the rotorcraft must incorporate two separate locking devices.
Since the transmission studs are not "removable" but fixed into the transmission case, then the fact that the attaching nuts are self-locking type should, I think, comply with the FAR/EASA.