As I recall, about the time the blood fractions thing came in, there were a couple of Gibbering Buddies who were seriously ill - cant remember their names, but it could be the reason...
Like the "adjustment" ON UNSCRIPTURAL VACCINATIONS, just before Nathan Homo Knorr went on his world tour including third world countries rife with typhoid cholera yellow fever and smallpox. He didnt want to come home in a coffin - but surely he wanted to be in heaven ASAP??