1. If the tabulation EC dataset would be an exact duplicate of the tabulation EX dataset, then the applicant may choose to collect data using either the collection EC or EX domain. 
  2. If an exposure is such that start and stop times are not required, and only 1 exposure date is collected, then the collected exposure date will map to both the start date (--STDTC) and end date (--ENDTC) in the tabulation exposure dataset(s).