There are no studies showing that the blood meal gets old, and there have been no reports of anyone saying so. However, I have seen some of the older brands (e.g., Nutrafin) of blood meal that have been stored for long periods of time.
It's very difficult to quantify the amount of "sour" smell in blood meal. However, I have had many customers who have noticed that blood meal has a "sour" smell. The blood meal that I use for my mixtures does not have a strong "sour" smell, but it is not neutral smelling either. Blood meal should not be used for a product where the scent of the food is important (e.g., bread or cake mixes).