Yeah, the volutes started small in 68, got big by 75, and shrank again until they cut 'em out in 78 or so.
The yellowing is not from cig smoke -- though a warhorse like yours probably saw a lot of that -- but simply for the nitro reacting to UV light -- it always turns yellow over time. That's why vintage silverburst LPs actually have a yellowish tint in the belly carve, too:
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FWIW, my 73 had already started yellowing by the time I got it in 87. Only surviving pic of it, with the rest of my rig at the time (1992 or so):
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