the best ones were made in 1966 (concidentally the same year I was born) =-)
of the early 1970s mk VIs i've played I found them nice (very very nice) players but tonal wise was a bit brighter than earlier VI models. Of course, I didnt' keep any sn# nor were i comparing multiple VIs A/B. But A/Bing normally against my CB, Coufs, VII, 875 or Vito that i had during those time frames and not directly against another VI - just somethime to keep in mind per my opinion ...