Body Types
Due to reasons such as country of manufacture, design improvements and what-have-you, toys change.  Jem dolls were not immune to this.  In the US and Canada, there are 2 distinctly different Jem body types: The short style (formerly called here the "Super Stars" or also referred to as the "Euro" body type), & the regular style (appears to be the most prevalent).  Besides those, there are at least two other styles (Mexican and Spanish). 
Thanks to Corey Bedford, Summer, Taffeta, and many others who helped contribute to this section.

Here you will see, from left to right, examples of: 
 
  • The short style (Synergy) 
  • The regular style (Jem).
  • The Mexican (Roxy)

  • It should be noted that the dolls were all standing level.  There is a very real  difference in height. 
  • Spanish style body (Not shown): is nearly identical to the regular body style (Jem/Jerrica in the photo left), body being slightly more matte and stamped "Made in Spain" on the back). 

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    The "Short" (aka "Euro" or "Superstars") Body Style
  • These seem to be a fair bit rarer in Canada and the United States than the regular size, but the regular bodies tend to be favoured, so as far as I know there is no value difference, just fun, variation related differences!
  • Most obviously, the doll is shorter than the regular body, the pelvic area is a bit thicker and smoother, as well the wrist joint is knobbier and the butt is a bit less rounded.  So far, all the short-bodied dolls I have seen have the smaller holes in the feet, but since regular dolls have the small or large holes in the feet, it doesn't seem to be body-type related. 
  • All the Super Stars dolls I know of that came with Jem bodies come with the shorter Jem body type. Thus, if you have a doll with the short body type, it could well be a Super Stars doll. Check for paint or hair stitching flaws/differences to figure out if you have a Super Stars Doll. 
  • Raya & Synergy are nearly always found with this shorter body. 
  • The "Regular" Body Style
    These are the typical Jem doll bodies, and chances are, if you get a Jem doll in US or Canadian packaging, it will have this body.  The body is (duh) taller than the "short" body style.  The wrists are less knobby, the pelvic area is a slimmer and allow more flexibility in front and the butt is more rounded.  They can have either small or large holes in their feet.  They are made in either China or Hong Kong. 

    The hands are different, they have little ball-shaped joints showing where normally Jem dolls don't! (normally they are more streamlined into the socket)
    Jem before the butt-master.... (the Regular body) Jem after!  (short body)  It's slightly more triangular shaped than the very round regular Jem butt.
    Large holes- found on regular bodies. Short bodies probably had these too.  Medium (found only on Mexican dolls) Small holes: found on regular bodies and short bodies. 
    The "Mexican" Body Style
  • The Mexican body is the easiest body to identify.  The defining Mexican feature is her body is super shiny and has NO Hasbro marks on it at all.  She has longer legs, making her the tallest Jem doll, but since her neck is a bit shorter, she's not as tall as she could be.  The limbs (on Caucasian dolls) are a pinker tone than regular dolls, plastic and vinyl seams are often very prominent. Not obvious in the picture, is the shoulders seem a bit wider/not pushed in as far than those of the regular Jem dolls.  They are lower quality dolls in general, it's quite common for the hands to be broken off or cracked.  Most Mexican's I've seen come with the smoother wrists, though my Mexican Aja has the knobby wrists (and, not coincidentally is probably my only loose Mexican doll without hand cracks!)
  • As for Mexican heads, there are two categories.  Both have the shiny bodies, but some have stamped heads (called Mexican Hybrids), others do not.  Both are considered Mexican dolls, but a true Mexican head (at least on this page, until it's been disproven) will have no Hasbro markings and will show signs of poor quality- make up flaws, very pale skin tone (in Caucasians and Shana), badly stitched hair.  I've noticed on all my non-stamped Mexican doll heads, the hair is sewn sparsely around the hairline- whereas every other Jem doll has a very dense hairline.  It appears that the Mexican hybrids used left over heads from the Chinese or Hong Kong factories. 

  • Read more on Mexican Jem dolls
    The "Spanish" body style
  • At this point I can only look to my Spanish 1st edition Jem/Jerrica doll for comparison (I don't yet have the others).  The differences are rather subtle and explained in fuller detail below.

  • Spanish 1st edition Jem/Jerrica ID page
    The body otherwise isn't too different, but I did notice her to be a little paler and even more matte than the Hong Kong/Chinese dolls. 
    The doll is marked © 1985 HASBRO INC./MADE IN SPAIN. 
    The legs are different though- on mine, she could not sit without making a "popping" noise (similar to bending the knees).  Overall it seemed as though the pelvis was just in wrong somehow- she even has a slightly pot-bellied appearance.  I'm not sure if this is typical of Spanish dolls or if I just got a particularly bad one.  The most obvious difference in her body is the feet- you will notice they are arched more than the average Jem doll's (far left is the Spanish foot)