Building test site, update dates (back date records)
I think I got it.....

SET hdIssues.IssueDate =  COALESCE(DATEADD(day,@NumberOfDays,hdIssues.IssueDate),null),
hdIssues.StartDate =  COALESCE( DATEADD(day,@NumberOfDays,hdIssues.StartDate ),null),
hdIssues.ResolvedDate =  COALESCE(DATEADD(day,@NumberOfDays,hdIssues.ResolvedDate ),null),
hdIssues.LastUpdated =  COALESCE( DATEADD(day,@NumberOfDays,hdIssues.LastUpdated ),null),
hdIssues.DueDate =  COALESCE( DATEADD(day,@NumberOfDays,hdIssues.DueDate ),null),
hdIssues.AcknowledgeDate =  COALESCE( DATEADD(day,@NumberOfDays,hdIssues.AcknowledgeDate ),null)


Coalesce seemed to work for me, I had no idea what coalesce was before but saw it in this example and read up on it here

Anyone know of any drawbacks to this approach?