in direct conflict with spock prime’s supposed desire restrict his influence on the timeline with his future knowledge, when he finds it important enough and it’s something that is inevitable anyway he doesn’t have a problem with discreetly giving out a few clues. the ‘fleet has a few of these hints on file that they’ll get around to eventually (leonard has no clue how they were going to get their hands on a couple of whales or what they would be needed for), but what they don’t know is that spock gave mccoy something off the books - the cure for a rare blood disease, xenopolycythemia. when leonard asked why he was giving this to him, spock said he couldn’t risk a cure not being found - it was too important. mccoy got it. kirk must contract the disease at some point. if it keeps his best friend alive that much longer, he isn’t going to rat spock out to the brass for trying to change the future.
it’s only later - years later, spock from that other world long dead - after testing his own blood and seeing the diagnosis, that he finally understands