This page assumes you already know what normally came with 1st edition Jem/Jerrica, as well as Mexican Jem (who also came with starcaps) and ID's only what differs between them.  Please note, I do not own this doll NRFB, so there may even be more differences than noted here.
1st Edition Jem/Jerrica is normally found with plain bulb earrings. But later in the production of the first year of Jem dolls, the Original Jem doll got star-capped earrings.  There seem to be a few variants on the 1st edition Star-Capped Jem/Jerrica, which are:

Some Star-Capped Jem's have pink star caps, others have clear. 

Odds seems to be about 50/50 as to whether you'll get the one with the plain old white/waffle weave tights, or the variant pink tinsel-y tights.

The face especially seems to be paler on these compared to the non-star capped version.

There seems to be a correlation between star-capped Jem/Jerricas and China made dolls.  Most Jem/Jerrica dolls (non star caps) are made in Hong Kong

Fredo, who acquired a star capped Jem/Jerrica in Puerto Rico mentions his belt having a pink fringe, similar to the fringe on Danse's jacket.

By the way, they are easy to fake, so buy from someone you trust.  As well, the earrings, bulby or not, are always called "Jemstar earrings", so do ASK a seller if they mean they are actually stars or just quoting the package before buying!

Zomboy writes that his starcapped Jerrica dress (compared to the non-star capped J/J doll) is "a slightly different shade of blue, more aqua, and the dress itself is wider and shorter. The hats got cut off in the picture, but the hat is much larger. The Jem dress that goes with it is also bigger, and comes with the bigger bracelet.

Antipathy's note #1: "Another characteristic I noticed with the SC Jem's is that their eye painting is improved (in my opinion).  The "half-moon" pupil's of the "regular" 1st Jem's--the feature that gives her that drowsy or zombie-like appearance (at least that's my conclusion)--are now more full like the rest of the dolls."

Antipathy's note #2: "Yet another potential characteristic is that the shoes are thick-sided.  The three dolls I have have all come with thick-sided shoes.  Both the Jem and Jerrica.  The Jem shoes also have a slightly strange matte feeling--almost as if they have been coated with something."

Antipathy's note #3: "One last detail (heh heh) is that one of my SC Jems came with a bracelet with a cabochon-cut "jewel".  I have never seen this in the various bracelets I have come across."

Thanks to Pete B for this photo and info.