When Derby Reference Manual, version 10.4, lists Derby limitations for DATE is said that the smallest DATE value is 0001-01-01 and the largest DATE value is 9999-12-31.
When the same manual explains the DATE function is said that:
"The argument must be ... a positive number less than or equal to 2,932,897 ... The result is the date that is n-1 days after January 1, 0001, where n is the integral part of the number."
Testing for the largest integer returns the expected result:
select date(2932897) from SYSIBM.SYSDUMMY1 returns 9999-12-31 -> OK
The problem comes when testing the smallest integer. We get a result different than we expect:
select date(1) from SYSIBM.SYSDUMMY1 returns 1970-01-01, but it should have returned 0001-01-01
The smallest date we get using integer as an argument to date function should be the same we get when using the smallest string representation as an argument. In other words date(1) should be equal to date('0001-01-01').
select date('0001-01-01') from SYSIBM.SYSDUMMY1 returns 0001-01-01 -> OK