Purchased this SKS today, the arsenal marking looks like a cross between the 636A and 636B examples in the arsenal marking chart. The right 6 has a base like the 636A drawing and the left like that of 636B. Has this been reported in the past?
(https://i.ibb.co/NnbLH2Th/1175.jpg) (https://ibb.co/zHDS0V6c)
It appears that year 22 /636\ guns generally have a version of this stamp like yours shows with the atypical stamp. I'm honestly not even sure where the A and B versions come from, in my files I only track them as /636\ with no distinction. Here's a grouping of them, I can't make out a definite A vs B or a transition year (maybe the second year 14 gun??? But then I have many other year 14s that show sharp corners on the 6's).
Year 13:
(https://i.ibb.co/zWpBCj9X/1304374-receiver.jpg)
Year14:
(https://i.ibb.co/jvxqTdjc/1400349-receiver.jpg)
(https://i.ibb.co/1YnzTNZt/1412261-receiver.jpg)
Year 16:
(https://i.ibb.co/3mFPZk5g/1616034-receiver.jpg)
Year 17:
(https://i.ibb.co/9m6C8vwR/1710383-receiver.jpg)
(https://i.ibb.co/7tt46vYG/1715453-receiver.jpg)
(https://i.ibb.co/XrHdmB9T/1323159-receiver.jpg)
Year 18:
(https://i.ibb.co/Z6bS6VWg/1827328-receiver.jpg)
Year 22:
(https://i.ibb.co/Cs629CF7/22047732-arsenal-stamp.jpg)
Years 26:
(https://i.ibb.co/zW2Lz8LR/26002172-arsenal-stamp.jpg)
(https://i.ibb.co/sJdLJPxL/26014787-arsenal-stamp.jpg)
LC will have to comment on it as I believe he was the one that coded them as A or B.
Thank you for sharing those photos, it is very interesting seeing the variety.