Petrol Injector Yellow Plastic Cap

Hello Gentlemen

I bought one injector seal kit, and it contained a yellow plastic cap which fits over the nozzle and can be held in place with a black plastic locking ring.

Is the injector to be installed with the yellow plastic cap in place ? (There is a small hole in the end of the cap)

The black plastic locking rings have disintegrated on all the injectors, so I fitted the injectors without this black plastic locking ring. (The Volvo shop only had the seals kit for one injector) Is this OK (If not I will need to order 5 more seal kits)

A simple question but your clarification will be much appreciated