Abbreviating Months in CSL if used with a Day?

Is there a way to abbreviate months in CSL using Chicago format, but only if the exact day is specified? e.g. "December 2019" and "Dec. 2, 2019"? I presume it's using <date-part name="month" form="short", but wasn't sure how to structure an "if" statement to correspond with the lack of a specified day.

Thanks so much!
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