For owners of Acer Aspire 5920G-934G25Mi-URGENT!

Date of manufacture would be different for different laptops even in the same series, also the firmware version. Drives used, even in the same model, are often different aside from the size. You are assuming that they are building that model using drives purchased at the exact same time from the same vendor, which is not always true.

That's true   I am desperate! Ok,at least I know what kind of logic board I need, so, the problem is the firmware. Is it possible to upgrade or downgrade it from western digital ?

There are firmware updates, usually from the laptop vendor. If not you can check with WD support.