In TSS, Q makes an offhand observation that seems rather strange. Going over briefing materials on Schrenk, he remarks, "He was described in his cover as a demolition worker, which was typically close to reality: he'd been trained at Norfolk in explosives." [5:33] Although I'm not sure what Q means by "typically close to reality," I think he's referring to a presumed match between cover identity and the actual skills an executive possesses, and moreover he's saying that this is the way cover identities are usually arranged at the Bureau.
Well, I'm afraid that it isn't "typical," as least with respect to Quiller. Below I've listed some famous Q identities from current and previous QBsOTM and some cover professions which don't seem to match what we know of his expertise:
* Walter Martin (aviation psychologist), TSP.
* Karl Rodl (auto mechanic), TSP.
* P. K. Longstreet (stamp dealer), TWD.
* Karl Dollinger (journalist), TWD.
* Charles W. Gage (geophysical consultant), TTB.
* Clive Wing (coin dealer), TMC.
* Paul Wexford (journalist), TKM.
* Kapista Kirov (representative for plastics complex), TSS.
I suppose one could stretch a point and say that, for Walter Martin, since Q is both a pilot and a rather good practical psychologist, "aviation psychologist" might not be a bad match. Nor is Karl Rodl too far off, since Q knows quite a bit about engines (though he almost gets nailed on the "hemispherical head" question at the roadblock). But...geophysics? Plastics? Stamps and coins?!
Contrary to what Q seems to suggest, the Bureau apparently has other reasons for choosing cover identities. In fact, the Charles Gage identity was chosen for TTB precisely because it would provide a reasonable rationale for Q *not* to have to say anything related to his job (secrecy, oil drilling, so forth). In any case, it is certainly not "typical" for the Bureau to match Q's cover occupation to his actual interests--not unless he has some hobbies and avocations of which we are unaware!