I own a Y570 which I had just purchased recently. After taking a look at the machine it appears that the machine came preinstalled with the BIOS version 47VN31WW (V2.09). However upon going therough the Lenovo support site http://support.lenovo.com, while going through the list of drivers there was a section for BIOS. Upon checking the BIOS details the version listed appeared to be a lower version than what was perinstalled. (47CN28WW (V 2.06))
Should I still proceed with the update to the lower version of the BIOS seeing that my Peinstalled version seems to be more uptodate?
The BIOS which your system came with is definitely newer than those provided on the web thus there is no need to flash the BIOS on the web.
Reasons why your laptop has a newer BIOS could be due to factory reasons and licence agreements with Windows. There have been cases previously where customer's laptop fresh from the factory has newer BIOS however the functionality of the BIOS are the same with the one available on the web. If your system does not face critical issues you will not be required to flash the BIOS unless it you are specified to do so.