"Part of the reason why the words in the 1977 version are so much clearer can be seen in the video: separate mikes for the voice and the guitar, and an appropriate balance between them (thanks, presumably, to someone on the sound desk). The later performance has, as far as can be seen, only a single mike."
yes, but sung unaccompanied, by a singer who has learned voice projection,there should be no need for a microphone.
any singer who cannot sing without a microphone and not be heard needs to go away and start singning from the diaphragm, and learn voice projection.
I am not against microphones,providing they are properly balanced[as they were not in the later version], but to be able to sing without them,is important,of course a different skill is required to sing with them,learning to hang back on popping ps and bs and not have sibilant ssssss.