[codeflo]

In theory, there's nothing stopping the OS from remapping the pages of your address space to different physical RAM locations at any point during your test. So even if you have a reproducible bit error that caused the crash, there's a chance that the defect memory region is not actually touched during the memory test.

Now, this may not be such a huge problem in practice because the OS is unlikely to move pages around unless it's forced to swap. But that depends on details of the OS paging algorithm and your server load.