I can't answer all your questions, but I can tell you then I'm using EC5s on my feather and so far I have got them all from Hobby King. I too had read about the different way around that supposedly genuine/non-genuine ones go together, but to be honest, they seem a bit of a pain to assembly anyway. The best way I have found to do it is as follows:

1) Slide the housing onto the wire.
2)Solder pin on to end of wire - Make sure all the solder is contained in the cup in the end of the pin. If any runs down the outside of the pin it makes getting it into the housing even trickier.
3)While the connector is still warm/hot I push it most of the way into the housing.
4)I then put a spare pin of the opposite gender on to the pin I soldered, turn the housing upside down and press the pin on to my workbench to push the pin into the housing. If you do it right it engages quite snugly with a 'pop' sound.
5)Remove the spare pin I used to put it in with.

No idea if that is the easiest way or if it is applicable to the EC8s, but its what works for me.