There's another way to always identify the official model year in the USA, and that's by the 10 digit of the VIN. It always identifies the official model year...regardless of the build date.
This tidbit of info comes in real handy when there's either an early or late roll out or a truncated model year.
The 2004 - 2006 model years are the E53 X5 facelift models...so look for a 4, 5, or 6 as the 10th VIN digit.
See the chart below for the 10th VIN digit and the official model year it represents: