Auto Rikenon 50mm f/2 M42 Lens Mystery

Howdy, APUG!
I noticed something a little interesting regarding certain Auto Rikenon 50mm f/2 M42 lenses that perhaps some of you might know the exact reason for.
I own three of these lenses, two of which have their serial number on the front of the lens and one that has the serial number on the side of the lens. The two with the serial number on the front are within #103XXX, and I've noticed that lenses before 103XXX and also a certain number sequence after have the serial number on the side. However, lenses with a higher serial number, such as one I currently saw on ebay, has the serial #117XXX on the front of the lens.
#102610 - Side
#103252 - Front
#103630 - Front
#105189 - Side
#117297 - Front
It makes me wonder, was there a certain reason for this? Were certain Auto Rikenon lenses made at a different location, etc?

Just thought this was a little interesting. I'd love to hear your insights. Thanks!
-Paul

To my understanding you are comparing apples to oranges, as I see two different barrel designs. Maybe there are even more differences.

But even if the lenses would be truly identical in optics and barrel, except for the location of the serial number, what would that tell?. The same manufacturer may have decided for a different location due to esthetic reason or for production reason.

@AgX
Thanks for commenting!
To answer your question, it probably will not reveal anything at all. Maybe it’s not strange, but just thought it was interesting that these lenses started with certain serial design, it changed, then changed back to original, then changed again. There could even be more changes.
I figured, just as you have, that it was probably due to some kind of production reason.

Also, I do wonder about the possible barrel design differences. That would definitely be interesting.

The barrel design likely is a matter of fashion. First peak&valley rings were common, then came flat rings covered with bandages with tiny tetraeders.

@AgX
Would you at all suspect a change the lens elements?

One never can exlude such. (But at least with major variations that would be easy to detect just by sight.)
But I would not exspect such.