Found this from another site for Diamondback bikes although this doesn't seem to apply to the 2005 OP's frame.

"The first 2 or 3 characters are usually letters. This identifies the frame factory (the frame factory is not usually the same as the brand). In many cases a Diamondback frame will show either ACs (Accell, the current owner of the brand) or K* (Kinesis, another big bicycle frame builder). There are other variations for other brands (Schwinn and GT frames usually start with SN).

The next 2 to 4 numbers tend to be the date of manufacture. 0911 would generally mean November 2009, but then again, there are variations.

The final 4 numbers is usually the production sequence... where that particular frame falls in the entire day production which may include several different types of frames."