I use MemTest86+ on every stick of DRAM I buy - if there's even a single error, it goes back as defective. The fact that this memory seems to work for most access patterns doesn't excuse the fact that it is completely broken for others, because good memory should be able to store any data and maintain its integrity for any access pattern.
Unfortunately even MemTest86+ is not exhaustive, as I found out while troubleshooting a very strange issue: a specific file in a specific archive would unpack with corrupted bits (and an "archive damaged" message) on a coworker's computer, but on half a dozen other machines would be fine. A hash of the file matched, so HDD-based corruption was ruled out. His machine passed an overnight run of MemTest86+ perfectly and AFAIK unpacking no other archives would yield corruption. He reported never getting any crashes - but yet, that one file in that archive would fail to unpack correctly.
It would always corrupt in the same strange way. On a whim, I decided to swap the RAM out and the problem went away. Even the "bad" stick seemed to work fine in other machines with the same model of CPU and mobo running the same OS and unpacking the same archive, but with his extremely specific combination of hardware and software, would always fail. That experience taught me that bad RAM can be extremely difficult to troubleshoot.
This isn't like other storage technologies e.g. SSDs where their finite lifespan and sensitivity to access patterns is well-documented. It's a case of claiming to sell memory while giving consumers a close approximation of one that completely breaks in some situations. I think it needs to be treated like the FDIV bug.