3 digit year problem

Hi,

Is there any rhyme or reason to these ISO format date parsing rules?

test=# select '1-1-1'::date;
ERROR:  Bad date external representation '1-1-1'
test=# select '69-1-1'::date;   date
------------2069-01-01
(1 row)

test=# select '50-1-1'::date;   date
------------2050-01-01
(1 row)

test=# select '40-1-1'::date;   date
------------2040-01-01
(1 row)

test=# select '30-1-1'::date;
ERROR:  Bad date external representation '30-1-1'
test=# select '100-1-1'::date;
ERROR:  Bad date external representation '100-1-1'
test=# select '999-1-1'::date;
ERROR:  Bad date external representation '999-1-1'
test=# select '1000-1-1'::date;   date
------------1000-01-01
(1 row)

Why can't someone store the year without having to pad with zeros for years
between 100 and 999?

What's wrong with 30-1-1 and below?  Why does 40 work and not 30?

Chris