I don’t think the difference between mono-orgasmic and multi-orgasmic is a semantic difference. If someone has an orgasm, they often know they do.
I can tell for myself as well, as a multi orgasmic person. It is true that when ejaculation isn’t considered the tell tale sign of an orgasm, the definition of an orgasm vastly expands, and in THAT sense it is semantic. An orgasm is essentially a user defined peak of pleasure. For me for example, orgasms often start small and get bigger, as the graph suggests. Maybe some of the small orgasms are just intense pleasure, and it is hard to draw a line as to where real orgasms begin. But at a certain point I am definitely having orgasm after orgasm, each one accompanied by a loss of touch with reality, a peak sensation, sometimes even hallucinations, lasting tens of seconds, or even for minutes at a time. Comparing these sensations to a traditional single ejaculatory orgasm, I can guarantee you that the difference between mono orgasmic and multi orgasmic isnt semantic as you suggest.
Check out the article you got the graphs from. It seems to say that multi-orgasmic-ness, is rare, and even suggest another level of orgasmic capacity that only 1 percent of the female population has. The study is limited in that it is only about women and that it is a case study, but read the accounts of the women in it and tell me if you think it is semantic