From some informal research I did on the archery archives website (which is sadly gone now), the 709 Hunter was from 1965 to 1967, and the 7090 Hunter was 1968 and 1969 only.
Also, the catalogs indicated that the 709 Hunter had green glass in 66 and brown glass in 65 and 67 - this would appear to contradict Blackhawk's age assessment of his bow, but I imagine that there was quite a bit of variability at the factory, so I would think serial number would be a safer way to date one of those bows.