...It's intuitively attractive that the various timelines would have this tendency to "drift farther apart" from each other towards the future, so quite possibly Spock arriving at a timeline that only split 25 years earlier doesn't even count as a proper crossing.
It's also intuitive to think in terms of "timeline distance" in general. Kirk and pals crossed universes in "Mirror, Mirror" - but also in ST4:TVH where they went from a timeline where Scotty had not made Madeline upset and thus changed the future of the entire Republic of Dasvidania, to one where he had. The two timelines don't appear all that different when viewed from San Francisco, so there's little "distance" there.
Whether it matters to our TOS heroes themselves that they hopped from one timeline to another by going through the split point, rather than by direct means, remains unclear. If using the points route does protect a time traveler, we lose the datapoints of heroes who have done that sort of a thing (that is, most of them) and are not suffering any known ill effects. But if the time interval traveled is the truly significant thing, then Georgiou has all of 'em beat (save for Spock and McCoy at Sarpeidon, and the two guys eventually made it back - and of course all the VOY folks who visited Big Bang and likewise returned to tell the story); the failure of others to show similar symptoms tells us nothing much, then.
Timo Saloniemi
