…We recently had a tank with a vindicator handwheel that always showed green (whether on or off). I am not saying this is a common issue with the vindicator handwheels, it may well have been an improper installation issue (it was promptly replaced, and the old one discarded, so we will never know). My point is that I don't think the vindicator is fail safe, and is no replacement for a proper flow check.
It is difficult to imagine failure without improper installation, probably leaving spacer washers where they shouldn’t be or installing one for the wrong valve manufacturer.
Nothing is failsafe including depending on DM with unknown experience and skills — some are great, some not so much, and all are newbies at one point. In the end, the diver is responsible. One thing for sure, a closed indicator on a single is likely to spark a conversation rather than the DM simply changing the valve which is understandably objectionable to many of us.