well you r right about parental or govermental control issues regarding the export of the mangas that might deemed unfit for children until the internet(thou even before that; ppl when they want something they usually get it regardless of anything. i know i did.) and about the need for a in-depth research about the explict material issue; i cant give you definitive answers or publicaitons(well i found them but i neither have time nor the inclanation to pay for an article that will have little benefit since i am neither a manga historian nor a critic) and the only research i did was a quick wiki 1. also u r right about these sub-genres being longer in japan then we may realize considering 800 years of history of manga. i can only give you relative numbers based on mangaupdates which isnt exactly absolute. but my point came from the censorship japan had on publishing these subjects for younger audience till the late 1980s.(which with increasing numbers of enjou kosai and such another bill passed in 2010) after the relaxation of censorship more and more such subjects started to grow from shounen demo(as u have mentioned with dragonball) and jumping to other demos.
The only Adult content I think woudl work is if it is warranted in a romance scene. Skip all fan service, leave it to the Shonen based stories. I am of the upper age end of the Josei community, and just the right amount to hint is all is needed.
but maybe fan service in the shoujo/josei magazines are different. Like a shower scene, or something. I dunno how that would really work but in RL that works pretty fine as a fan service directed to the female viewers lol.