I'm guessing this is not a period Avocet saddle - meaning a knock-off.

I remember the 80's as being the golden age for Avocet stuff. Not only saddles, but cranks, etc.

The screening in the first two photos doesn't look right, esp. the second. Too bright for age.

Since it has a round-top adapter, I'm guessing it came on a lower-end bike, and the seller didn't think to remove it before taking photos.