I would import them as character then deal with them in SAS. You can check the values and convert them depending on the source value. For instance you can check if the first character is numeric then create a date using the first value* as the year, and the second** as the month in the MDY function. Conversely if the first character is a letter, use the first value as the month and the second as the year in the same function. You'd have to supply a value for the day as mentioned in the previous answer.
* scan(date, 1, '-');
** scan(date, 2, '-');
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