Can't help you with the dating, but as for the open-comb design, it's still got a following - in fact I think I prefer it. I don't know what the "official" reasons are for the open comb-design, but in my experience, it gives a closer, easier shave. The cutting edge of the blade seems better lubricated by the soap (because most of it's not been wiped away by the closed-comb or safety bar) and also the open comb doesn't flatten down the stubble as much before the blade gets to it.
Those are my feelings anyway - I'm sure other luminaries on this site will give their thoughts too.