My older one is also from the early-mid '80s. No blue color but it's identical to my newer one and probably identical to yours too. The velcro cups just fit over the same old heads that we used to wrestle the old-style pads over. Only visible difference I've seen in recent years is the switch to the black sheath over the handle (as opposed to the clear ones).
AFAIK, they haven't really changed the basic Model 5 (housing, etc.) at all over the years but I've seen some pics of older Cyclos (as in, from the '50s or so) that had metal top handles (instead of plastic) and cool looking engraved metal ID plates (instead of the stickers). Also no grounded plug or plastic sheath over the handle. That's what I meant by "more machine age", but I guess the differences are pretty subtle. I would like to find one of the three-headed ones from that earlier era, though. And if the one we're all used to is the Model 5, what are the Models 1-4? Heh heh, if I'm not careful I'll end up collecting the things