I don’t know much about Vegans and don’t really care one way or another. However, I know one female vegan and you describe what happened to her perfectly. She’s pretty messed up physically because of her veganism.
That’s too bad. The effects of B12 deficiency can take time and are not necessarily obvious. And when the damage isn’t permanent, it could still take quite a bit of time to recover from the deficiency. Slow to replete, slow to restore. That’s my lay understanding.