Pelikan 21 Silvexa Information?

[tutu11]

Have a good day,
I recently came across a "Pelikan 21 Silvexa piston filler with 585 OB gold nib". Do you guys have any information on this pen, about its history and place in the lineup at the time? I tried Google but didn't get very far. Thanks in advance!

[duckrider]

https://www.pelikan-collectibles.com/en ... ng_toc_j_2
http://www.fountainpennetwork.com/forum ... formation/