Can't be of a whole lot more help, but I would suggest more like the mid-80's. Any more specific info would likely have to come from the BATFE. When Detonics went out of business, by regulations, they would have had to turn the "books" over to the ATF.
Soooo... if you're really into it, find out the necessary legal chanels under the "Freedom of Information" act and requisition copies of the ATF log. I'll bet everyone in these groups would posititvely LOVE it if someone figured out how to do that.
...Deeton