Determine Combined Prefix
**Note 1:** Combined Source of 1 or 2 indicate the Combined fields is based on the Clin field or Path field respectively.
Combined Source of 3 indicates a combination of data was used to set the Combined value. For example, 4a and 4b were combined to derive 4c. The prefix will be set to 'p'.
Combined Source of 9 indicates the source is Unknown. It should only occur if the value is 88. No prefix will be set.
**Note 2:** If the source is 1, but there is no clinical prefix, c will be used. Similarly, if the source is 2, but there is no path prefix, p will be used.