If the 1999 SAE J300 standard raised the HTHS requirement to 3.7 cP for a 15W-40 oil, what was gained by raising the CI-4 to 3.5 cP?

It bumps up the requirments of the lower J300 oils to the 3.5 requiremnt. Since SAE J300 requires that your 15w40 to have a 3.7 HTHS, you gain NOTHING. But all the other and thinner weights,like 5w40, 10w30, and 10w40..... have lower SAE J300 HT/HS requirements that get bumped UP to 3.7 with CI4(plus) spec!