In 2006, the SARB013, SARB015 and SARB017 were introduced and became an instant success; especially the SARB017. Each identification number represents a different colour: cream, black and green. The SARB017 (green) model became by far the most popular because it is unique and can be worn in literally any situation, business or casual. The other two variations (especially the creme SARB013) are now much harder to find, making them more valuable and collectible today.
All of the 2006 models use an 6R15 Automatic Diashock 23 Jewel movement, provide 20 Bar water resistance and have gold plated hands and numbers. These three models are the longest running models and continue to gain popularity because of their elegance and versatility. There are only a few subtle differences between the three watches. For example, both the cream and green versions use a more traditional hand system with a cathedral hour hand while the black version uses a more modern look which compliments the intense colouring.
However, Seiko as of 2013 has upgraded the 6R15B movement to 6R15C and D eventually. The upgrade includes:
1) Adding one jewel to the main plate, barrel hole (6R20 has that jewel already)
2) Modified ratchet sliding spring
3) Modified date indicator maintenance plate
4) New balance wheel
5) New barrel
So, early production of 6R15C has 23J, the late production of 6R15C has 24J. Adding a jewel and modifying the ratchet spring are all related to the upgrading of the barrel (to higher power reserve, so higher torque). The modified date plate is due to complaints of date misalignment. Seiko with this upgraded balance wheel might aim to increase long term stability. The previous 6R15s all have difficulty maintaining long term (1-2years) stability in accuracy.