What I’m wondering is whether the backed up MBX files in fact did contain those emails, but because it’s “too much bother to look for a particular email” they never tried restoring MBX files then scanning them.
I’m not so sure that it is a case of “too much bother” so much as a case of destroying evidence. The efforts to recover any information will be full of sound and fury, perhaps even frenzied activity, but will (intentionally) come to naught. Even IF the e-mails are found by someone within the administration, I’d bet those files will be (illegally) purged as well.