Vega 3 for Zenit 4, 5

This lens was standard issue for Zenit 4 and Zenit 5 camera.
But it's nothing standard about this lens. Seems like KMZ change design of this lens every month.
Were they not happy with original design? Did they try something new every time? Did they try to customize expensive Zenits 4 and 5? Did they catching the fashion? Who know!
I believe many more designers of this lens exist. Please fill up the blanks!!!
Focal length-50mm
Relative aperture - 1:2.8

Aperture is automatic preset by the camera's electro-mechanics.
Aperture type is instant.