In theory, could blood loss, such as that which occurs during childbirth, be a cause for b12 deficiency? i.e., if a person developed iron anemia due to blood loss, could that eventually lead to chronic low b12 levels? any connection here?

No connection. A variety of causes of Vitamin B12 deficiency : Loss of part of stomach, e.g., weight loss surgery; atrophic gastritis, pernicious anemia; use of proton pump inhibitors such as Nexium and Prilosec; heavy consumption of alcohol; Crohn's disease, Celiac disease.

No. Blood loss causes iron deficiency but not B12 deficiency. Liver has enough store of B12 to last more than a year. If you drink milk and eat any animal proteins. you would get enough B12,