The two main problems I see with doing what I think you want to do with an INFORMAT are what you are inputting and what you are outputting. You are attempting to define a character informat but the MMDDYY format is a numeric format. It outputs a numeric date not a character string. You are attempting to define the inputs as date constants, but informats need character strings as inputs. That is why it complains about overlapping ranges. '01JAN1990' is less than '01JAN2007' which is less than '31DEC2004' because '19' < '20' and '31' > '01'.
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