Reports of, is not the same as have been. Never replicated, never verified.
They have, actually. It is just that most people don't know about it. See below.
Those are old wive's tales that have been debunked...
Before you throw caution (which costs nothing) to the wind, I would be very interested to hear the nature of the debunking evidence you've referred to. I've never encountered any actual debunking of this particular claim, but rather just the anecdotally-based assertion that because the claimant hasn't ever heard of or experienced or found reports of one of these events himself, they don't exist. It's a little like claiming that just because you've never witnessed a rogue wave sinking a ship means they don't happen. Scientists thought that was so for a long time, for lack of surviving witnesses or adequate predictive modeling, before
modern instrumentation found incidents of them occurring. You have to bear in mind that when handloaders have a gun blow up, they are likely to believe they caused it with an overcharge or the wrong powder and then pull down the remaining loads. It's embarrassing for them and doesn't typically make the evening news, so data from the field is hard to come by.
However, in the laboratory is another matter. The late Dr. Lloyd Brownell, who did all of DuPont's academic research on powder and pressures, reported occasionally measuring pressures in his lab for powder charges in the 30-40% case-fill range that produced more than double SAAMI pressures, despite being "reduced" loads. He brought this up in a letter to the editor in Handloader as a rebuttal to a similar claim to yours, but as presented by a writer in a Handloader article in the late '60s or early '70s time frame. I have it somewhere on a CD of old articles about pressure that Wolfe publishing used to sell. Brownell pointed out these events are statistically rare in their frequency of occurrence. The erratic pressures produced at those load levels have standard deviations of pressure such that the likelihood of such events is very low. Just not zero. This means even higher pressures can occur, but still less frequently. One of the advantages Brownell had over other tests that I've seen mentioned, is years of funding by DuPont that allowed him to fire the many tens of thousands of rounds with pressure measuring that you need to shoot to have enough of these events happen to be sure you aren't kidding yourself. Most claims to the contrary, if not simple anecdotal claims that low charges are safe, turn out to be based on tests with too few samples to be likely to produce an example.
The bottom line is that there's no harm in erring on the side of caution, but there is potential harm in failing to do so, so the risk isn't equal on both paths. It also puts the debunker in the position of having to prove a negative, which is extraordinarily difficult and which is why I asked about the debunking.