There’s a bit of a problem with the theories as to why the lower dose gave better results. Live virus vaccine potency is measured by the titer of the number of live virions per milliliter. This is usually in the millions, and is expressed logarithmically. Decreasing the potency by half is a very small change in the potency, and is within the allowable decrease in potency during the “shelf life” (refrigerator life, actually) of the vaccine. No one suggests that other vaccines, including the many viral vectored vaccines used in veterinary medicine, actually GAIN effectiveness as they age. Vaccines are wonderful, but they are not fine wines.