What records are available that might contain someone’s blood type?
Blood types can be helpful in determining paternity or non-paternity. Obviously, we would prefer to use DNA tests, but for people who have passed away without being DNA-tested, and especially if they had no (known) children, then blood types could be useful. Blood types cannot prove paternity, but they can disprove paternity. For example, a type-O mother cannot have a type-A child with a type-O father or with a type-B father. The father must be someone with blood type A or type AB.
Blood typing was invented in the early 20th century and was used on a limited basis in WW I and probably wasn’t widely used until the 1930s or 1940s, so it would obviously never be available before that time period.
The records I know of that might have blood type are dog tags and driver’s licenses.
I also imagine that blood type might be on some birth certificates. That won’t help in my research since birth certificates in Georgia, where my family is from, are subject to privacy restrictions, The only ancestor for which you can legally request a birth certificate in Georgia is your parent.
Are there any other likely ways of determining the blood type of deceased ancestors?