The new box numbers were created to help 911's Sprint link them to Starfire. In their system they use station numbers. When Sprint sent the station number to Starfire as an address, it had no idea how to convert it to a street location.
Now, the station numbers are part of the box number. (e.g. station 24 in Brooklyn is box 7024.) In Queens , however, we're using 400 series boxes since they already had a 7000 series.