Note
that such an exceptional use is normally restricted to the usage of whose as a
relative pronoun

'Whose' is generally restricted to usage as a relative pronoun, however, their crappy text books state that it's quite normal to use it as a possessive adjective of 'which'. As Amused cited, it may be used frequently enough in the likies of Milton, Chaucer, Dickens and Shakespeare etc, but I believe that it's rarely, if ever, used these days, especially in spoken English. That said, NES who use this board come from different parts of NES countries. It's therefore not beyond the realms of possibility that 'whose' may be used, in the way I'm discussing, in certain areas of these NES countries.