In a 999 transaction, what is the correct way to indicate that the original transaction contained a field value that was syntactically valid as per the baseline control standard but violated a pattern specified in a TR3 Implementation Guide? Consider the case of an 005010X222 837 claim which contains the following segment in Loop 2400.

DTP*472*D8*05/23/2024~

The DTP03-1251 data element type is AN so the value is valid on that basis, however it clearly invalid on the basis of the format set in DTP02. When the payer returns a 999 transaction to report the error, how should they set the IK403 (Implementation Data Element Syntax Error Code) field? The two options appear to be "8" (Invalid Date) and "I12" (Implementation Pattern Match Failure). The "8" code is more specific, however I suspect that was intended for use with DT type. Can the "8" code be used to report an error in an AN type data element? The "I12" code is less specific and in practice probably less helpful to the provider that submitted the bad claim, but it might be correct here because it's an "I" series code and the DTP03 value didn't match the pattern defined in the implementation guide.