What's the difference between ORA-01843 and other date conversion errors like ORA-01861?

ORA-01843 specifically means the month component of the date string is invalid (e.g., 13, or an unrecognized month name). ORA-01861, 'literal does not match format string,' is broader. It indicates a mismatch between the entire string and the expected format, which could be due to an invalid month, but also incorrect day, year, separators, or length.