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Back in the 1980's, certainly not all usa fans used three separate terms to categorize sexy stuff. To some fans, there were only 2 terms: non-porn and porn. To others, there was non-porn, hentai, and porn. To the most knowledgeable and experienced, there were three distinct areas besides non-porn: ecchi, hentai, and porn. Back then, it was generally accepted on GOPHER, FTP, and USENET that "ecchi" was sexy stuff not as extreme as "hentai". The "ecchi" term came from the romanized sound of the letter "h" from hentai.
The image here would have been "hentai" or "porn" (depending on audience) back in the 1980's, but is merely "ecchi" on today's 4chan.
Generally speaking, in the 1980's, if the hentai illustration showed vagina, it was porn. If it showed naked breasts but no vagina, then it was still hentai.