I think when Dylan was doing the early stuff, folk-style, every word he sang was crystal clear. Videos of his acoustic performances at Newport and elsewhere in '63, '64, and '65 will back me up on that. When he started doing the electric music with a backup band then, yes, the words got a lot harder to hear amidst all the instrumental noise, and that was part of what his folk audience was objecting to. In my case I like Dylan's lyrics so much that I pretty well always know them in advance anyway from listening to the records, so no matter how loud the band gets in a live performance, I can still follow Dylan's words, but it may have been quite frustrating for an audience that didn't know the lyrics that well.

His diction got less clear in the 80's and from that point on I'd say, right up to the present, but that also depends on the night. In some concerts he is much clearer and easier to make out than in others.

Be that as it may, I saw some marvelous Dylan shows in the 80's. By the early 90's his voice was clearly deteriorating. The last show I saw, about 3 years ago, the music was great but his voice was a shadow of what it once had been.