The images were published in Spanish Penthouse in March of 1981, under the name of Vivianne Pollentier.
There is some controversy about the notorious open-leg shot with the enormous bush. There is one version where the hair does not cover her so completely, and another with a massive bush covering everything. Either way, she had a lush tangle of hair. I don’t know the back story, but this one is an untouched scan straight from the Spanish Penthouse, and it matches the less-hairy version. I don’t know where the ultra-hairy one came from, or why it exists.
Demi has tried to contain the internet presence of these pics by claiming she was underage at the time. That is the usual pretext that people use when they don’t want other people to see certain images, but in this case it may be true. One thing certain is that she was no older than 18, because she was only 18 years and four months old when the Spanish Penthouse hit the newsstands, so either she was 17 in the photoshoot or had just turned 18, because there is obviously a time-lag between posing and publication. (The Spanish text accompanying the photos says that her fictional alter ego, Vivianne Pollentier, was 23, and born in Lyon!)
She was a married woman when those pics appeared in Spanish Penthouse. Wikipedia says she wed Freddy Moore on February 8, 1981, when Demi was barely 18. Other sources say they were married in 1980, but the 1981 wedding date is probably the correct one. We assume that Demi posed for those shots at some time in late 1980, and she is wearing an engagement ring in the photoshoot, but no wedding band.
Her 1978 yearbook says she was a sophomore, so she was in the class of 1980 and would have graduated at about 17 and a half. If she had stayed in school, it probably would have been just after graduation when she posed for those photos.