From my books it looks like the 16800 was introduced in 1979, one year prior the 16660. Is this a fact or did they actually come out same year?

I am looking for a brother for my 16660 from 1980, which turned out to be one of THE VERY FIRST ever produced judging from the serial number. Ergo it would be a true pearl to find one of the earliest 16800s as well for that perfect match.