Visible Man/Woman

Did Revell first produce this model in 1972 or 1977. And, if it was manufactured in both of those years are there any significant differences? Would it be worthwhile to buy one of each? I want to begin collecting sealed anatomy models from the 1960s through mid-1970s, but don't know where to start other than searching and comparing what I find on eBay.

Thanks to anyone who responds,

Scott