Dating Artimide Mangiarotti Egina sospensione pendant lamps.  

I just found a pair of Mangiarotti Egina sospensione pendant lamps in excellent, but extremely filthy condition. Studio Mangiarotti says these were designed in 1979, is there any way to tell how long they remained in production? Can the Artimide labels give any clues to manufacture date? The level of dust, dirt and paint splatters make it hard to imagine they're not early models. Looking at online auctions, it appears that there were several sizes made. Are some of the sizes more common than others? The glass cones on mine are about 38cm across by about 17cm high. Thanks for your help.PS: Has anyone had good luck getting useful info about old products from Artimide? I might try sending them some pics.
<img class="wpforo-defau