I dunno if the Hinomaru were actually maintained better or if they were simply in better shape because the green paint acted as a primer and was also protected from the elements by the red paint of the insignia, which also could have been of a higher quality as well...
Also, I don't know if the Hinomaru were painted directly onto the green paint or the green paint was applied after the Meatballs were applied and then masked...
Judging from other Japanese aircraft that were either painted in aluminum or simply left unpainted, it would seem that the Meatballs were applied directly over the aircaft skin and other colors later applied in the field to tone them down, same way we did it with ETO fighters that were moved forward and based in France after D-Day...
I'm probably over-thinking it...
A word or five about the weathering..
I used the old school "Rubber Cement Masking Method" to achieve the chipping results. After spraying the model with Wal-Mart's "Color-Place" Aluminum, and letting it cure, I applied some rubber cement in "random but logical" areas of the model, using the cap-brush to put it on in a stipling/stabbing motion... I also used a smaller, 1/4-inch brush to do it in the tighter ares...
Once it was dry, I appled the grey on the undersides, let it cure, then rubbed off the rubber with my finger, exposing the aluminum underneath. I then masked the underside, and commenced to appying the rubber to the top-side...
Once the top was dry, I shot it with Model Master Dark Green, FS 34079... This's a bit lighter, about a shade, than the Tamiya JA Green, XF-13. I went with the MM color as I plan to "sun-fade" the upper surfaces as well as do the usual washes and drybrushing, since this model is a land-based IJN aircraft. So it was exposed to not only salt air and high humdity, but constant sun and sand-blasting from coral runways and the resultant dust... (The Japanese Navy didn't have much in the way of hangaring their land-based aircraft.)
I then did the same thing again, stippling/stabbing the upper surfaces with the cap and the 1/4-inch brushes.. However, I wrapped a finger in masking tape and pulled up some green paint with that, too.. I was able to control the amount of paint that "chipped" with that method too.. The real trick is knowing when to say "STOP!", lol... I kept getting to "just ONE more spot and I'll quit"... Fianly had to just walk away from the bench, lol..
It's just a different way of doing the "Salt-Masking" type of chipping paint, but I've been using rubber cement to mask since Christ was a Corporal, and I think the salt-masking method was basically just re-inventing the wheel... Having done it both ways, I saw no advantage to the salt and even had problems with it's removal in some places, so I keep it "Old School"... Dunno how old, but Shep Paine mentioned it (the Rbber Cement Method) in his book, How to Build Dioramas in 1980-something, and he referred to it back then as "The old rubber cement masking trick"... So I fugre it's another "oldie but goodie" from the model railroad community, probably from around the '60s