@Aletheo
As @JuppKowalski has said it is just a matter of design. The card design is different for each "collection" (iStripper, iStripperXXX, iStripper Classic, iStripperXXX Classic and VirtuaGirl) and within the iStripper and iStripperXXX collections it changes with the year in which the cards were released (I can't swear that the changes always occurred at the start of January, but that correspnds to my recollection and with the few cards that I checked).
One ***** point, a small number of cards (27 at the moment) are so called Special Event Cards (often referred to here as SECs) and these incorporate a gold star in their "badge". Though they appear in the Girls Store you can't just buy them as you can get them by other means - see the many discussions in the forum on this subject. As a new user you can simply ignore them as, despite their name, there is nothing special about them once you have obtained them.
As you have a small collection you can see this by going to the Girls Store and using the Collection and Release Date filters to see the designs used for each collection separately.