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:

Year14:


Year 16:

Year 17:



Year 18:

Year 22:

Years 26:


LC will have to comment on it as I believe he was the one that coded them as A or B.