“expected survival by three months”
“Expected” by who, based on what???
Doctors have a high rate of failure at predicting life expectency, and bean counters are notoriously motived by worst case estimates.
““Expected” by who, based on what???”
Typically, that would be either the average life extension observed during the stage 3 trials of the drug or procedure, or that observed during post-trial use. It is just the average - some will live longer, some not as long.