This is how low my 1985 Custom is - much lower than the current specification. I'd also put money on it it's never beeen changed since it left the factory 33 and a bit years a go. My suspicion is the early guitars either had a lower neck angle than is seen today (or were made with a more variable neck angle so some were low, others higher) or that over time that the guitar has had a bit of 'neck rise' (a known phenomenon on old Les Pauls). I had a slighly earlier guitar than this and that one was exactly the same - a very low neck angle needing the trem to be set right down to get a sensible action (that one I had to re-set as it had been messed around with the two outer screws down and the four inner screws up like an old Fender set-up). I also used to own a very early 1986 Standard where the trem was set much higher on the pivot screws as the neck angle was much steeper. So I think you have to set the trem height to the specifics of your own guitar using the specs as a guide / starting point. And yes I know it could do with a dust.