Chronic B12 Deficiency & Trauma Symptoms

Vegan for 15 years. My B12 was 158 back in 2022, and a recent test showed it’s only at 200, so I’ve likely been dealing with a chronic, long-term deficiency.
I also manage ADHD and C-PTSD. Since this low baseline is all I’ve known for years, I'm wondering how much it’s been flying under the radar and worsening my symptoms—and how noticeable the turnaround will be.
My doctor just prescribed B12 injections. I'm really curious if.