Just means that the X5 project was started before the X3 project was.

Remember, the Z4 & X3 were probably BMW's shortest development times. I remember reading that the Z4 took only 18 months from inception to production - which is intrestingly short period of time for vehicle development (most take 3-5 years). Since the Z4 & X3 are related, I am pretty sure BMW it had a short development time also.

Also to note, the Z4 & X3 were basically complete carryovers from the E46 3 series platform (X3 got many parts directly from the 330xi with little modification). The E70 is no longer a straight copy of its 5 series parent, unlike last time around (E39 -> E53). It seems BMW has put a lot of engineering and work into the E60's child...

On another note (maybe scott can answer this), I have been wondering why there is such a huge influx in development numbers lately. BMW used to progress slowly, with small gaps that were easily explained (there were development codes for electric cars, the coupe version of the E39 5 series, etc...). But lately BMW has jumped from E65 (current 7) all the way now to F10 (the development number for the next generation 5 series). Thats 45 developments/projects, which maybe 15-20 of which have turned into actual cars... Scott?