Q. I have been under the impression that extensions on a date (st, nd , rd, etc.) are proper when used simply with a month (January 15th) but are not used in connection with a year (January 15, 2009). Please advise if this is correct or provide instruction to the contrary.

A. Chicago style doesn't include the extensions in either case. When the ordinal is called for, we spell it out: the fifth of the month. That said, the style that you describe is common and not incorrect.