Must have led a sheltered life

I have previously queried Peake's and Coleridge's use of ‘must have V-en’ in the main clause of past-tensed conditionals, e.g. ‘the Ledge at the bottom was [so] exceedingly narrow, that if I dropt down upon it I must of necessity have fallen backwards & of course killed myself.’

After a quick search for ‘must surely have’ in the British National Corpus, I'm reluctantly coming round to the idea that I have indeed just led a sheltered life when it comes to this construction.  Witness:

‘But for the Munitions of War Act of July 1915 which enabled the Board of Trade if necessary to impose arbitrated settlements on unwilling employers, the union's policy of patriotic co-operation must surely have failed’ – Arthur Marsh & Victoria Ryan, The Seamen: A History of the National Union of Seamen (1989).

‘Science and technology must surely have progressed in a different way if these principles had been embraced from the start’ – Storm Constantine, Hermetech (1991).

‘Had it not been for their masks, the Phantasms' faces must surely have blistered – a gulf of rising furnace-air yawned beyond that hatch’ – Ian Watson, Warhammer 40,000: Space Marine (1993).

‘Had it not been for the psychic tracer, they must surely have lost themselves in the labyrinthine entrails of what was not one vessel but many’ – Ian Watson, Warhammer 40,000: Inquisitor (1993).

I don't know whether to make anything of the fact that three of these are from the trashier end of sci-fi (and that two are even from the same author) even though the search was conducted over a wide variety of sources.  If I ever find the time, I'll try wading through the vastly more extensive search results for ‘must have’ simpliciter.