Who knows? I bet they have.
It probably depends on how near the borderline you are when it happens. If flying a VOR approach with a cloudbase of say 1500ft (which is what I had when I first realised something was really wrong with the VOR receiver) and no terrain around, it doesn't really matter - apart from ATC wondering what the hell you are doing.
But elsewhere it might matter.
Obviously the important thing is to have a separate situational awareness source. A moving map GPS is the best by far. If flying an ILS I would tune in the runway extended centreline as an OBS on the GPS, and the LOC intercept should take place exactly on that line.
This would have been a much bigger issue in the past because even airliners did not have GPS until very recently. But then airliners don't fly much to places like Kathmandu
And when they do, they don't need a duff instrument to hit the terrain...
Now, in addition to the legally required 30-day VOR check (which is a formality because I usually fly with some VOR tuned-in, anyway) I get the avionics tested a few times a year (unofficially). I would like to be able to do it myself but while the testers (
example) do come up on US Ebay they are still 4 figures, and I can get the test done for about 1% of that.
There have been some interesting cases in the USA where a number of pilots flying with a specific MFD, which has incorrectly colour-coded terrain depiction, have hit the rocks, at altitudes corresponding close to the colouring errors. Admittedly this was a stupid pilot error (what is "MEA" for, etc?) but the manufacturer was completely uninterested in fixing the colour coding. Presumably they did not want to fix it because doing so would be an admission of liability.