Nvidia apparently changed to 500-series OEM GPUs to entry-level 600-series versions.
Nvidia is recycling aging Fermi chips and offers them in a new wrapper. The GeForce GT 520 has turned into the GT 620, but comes with just half the memory 512/1024 MB instead of 1024/2048 MB. However, the new card now supports OpenGL 4.2 and not just 4.1.
Also "new" is the GeForce 605, which replaces the 510 model. The card drops the graphics clock speed from 810 to 523 MHz and the processor clock speed from 1620 to 1026 MHz. The texture fill rate declines from 6.5 GT/s to 4.2 GT/s. The 605 also comes with only half the memory of the 510 and is available with either 512 MB or 1024 MB. While the original cards were rated at a power consumption of 29 watts, the 620 draws 30 watts and the 605 draws 25 watts.
It is interesting to note that that the "new" cards are launched in the 600 number range, which suggests that they are based on Kepler architecture. Even on the Nvidia product page, the 605 and 620 are listed as being in the same family as the new "Kepler" GTX 680.
Nvidia's Bryan Del Rizzo confirmed to Tom's Hardware that both the 605 and the 620 are based on Fermi architecture. However, these are OEM cards and they won't make their way into retail and mainstream buyers may not really care whether there is Fermi or Kepler card in their PC.