All the Japanese manufacturers preclude CG-4 on oils here in Australia, which is ridiculous.
There are thousands of Japanese small diesels running around this part of the world with oils that list CG-4, CH-4, CI-4, CI-4+ on there spec sheets without failure.
There was a problem at the time of CG-4 introduction, and for the life of me I can't recall what it was, but CH-4 quickly overcame the inadequacies.
Typically, Japanese manufacturers also demand higher calcium levels (IIRC, 3000ppm+) in their oils, but a lot of modern oils use other AW additives that work as well. If possible, pick a DH-1, CH-4 oil with higher than 3000ppm calcium levels and you'll cover all bases.