I have just read a post in russian (using Google Translate).
The poster is/was an employee of the KMZ (Krasnagorsk) plant.
He reported that the quality of the glass of most (all?) lenses changed over time, and that every time the technicians did complicated calculation to adapt the old project to the new glass.
After the plant restarted the production of non-military stuff after 2012 the new computers allowed to do the same calculation in a very short time.
Equipments for the military and "special' lenses (like those with all the zeroes in front of the serial) were assembled/tested with special care.
People going for these collectibles may have a point
Sub-models with a long life, like some of the Helioses, could have seen improvements/recalculations that weren't actually reflected in a change of name.
There might have been differences between examples coming from different plants. KMZ ones are believed to be better...
I'm kind of doubtful that most of these differences/adjustments can actually make a discernible difference, if the vintage is more or less the same.