I can see the MS Shell Dlg 2 font in version 5.44, viz:
But I cannot see it in version 6.2.1, viz:
FWIW: it's not in Word either
In this context, I assume that the critical difference between calibre 5.44 and 6.2.1 is the version of Qt that calibre is using. But I haven't a clue as to the underlying cause of the absence of the font in calibre version 6.
I suppose I should have a peek in my registry, here 'tis:
BR