This 'end of April minus a month' query returns no records:

SELECT F_PROCESSDATE
FROM T_LIMZ1_SAMPLES
WHERE F_PROCESSDATE Between cast('30.04.2002' as date) And (cast
('30.04.2002' as date) - 31)

And yet this 'start of April plus a month' returns 2000+ records in
the correct date range to 1-May-2002:

SELECT F_PROCESSDATE
FROM T_LIMZ1_SAMPLES
WHERE F_PROCESSDATE Between cast('31.03.2002' as date) And (cast
('31.03.2002' as date) + 31)

Why can FB successfully add 31 days but not subtract them?

Regards,
Andrew Ferguson.