TH you are correct if the shrouds are fittted, but we did not fit and forget the shrouds they were only fitted when deemed necessary.
The 18 Sqn incident the missing droop stop was not noticed because on shut down the LM does not check them like the americans used to i.e. he is inside monitoring the rotor brake for over heating/fire on shutdown and you are quite correct though in that if the shroud is fitted you cannot see the droop stops, the fire hose would not work and the first you would know is the big bang.
I was on top of an aircraft two down from the 18 Sqn one, doing independent checks prior to another rotortune flight and it shocked me, thankfully no-one was hurt.