There is one more thing to notice about the first query.
You assign the value "2000-02-01 12:34:56.789" to @EndDT but the query returns "2000-01-02 12:34:56.789".
Either make sure you are using "SET DATEFORMAT YMD" or use an unambiguous date format for the string literal "2000-02-01T12:34:56.789".