Well the 1 billion (actually just 1 short of a billion unless you also assign zero) would be true if no other rules were imposed, just assign each in order, but the power that be
were not up to snuff on their logic.
If the 1st 3 determine area of the country and the next 2
determine month and year issued then for any given region
there are only 9,999 unique numbers.
That’s unique per region and month/year anyways.