How to include concatenated values in a dynamic pivot column value?
You can use REPLACE on the date column in the @PivotColumnHeaders string to build the concatenated column. 

SELECT @PivotColumnHeaders =  
   COALESCE(
     @PivotColumnHeaders + ',[' +  cast(SystemFullName as Nvarchar) + ']',
     '[' + cast(SystemFullName as varchar)+ ']'
   )
FROM System
WHERE (@SelectedSystemIDs IS NULL OR  System.ID IN(select  * from dbo.SplitInts_RBAR_1(@SelectedSystemIDs, ',')))     
AND ((@PlatformID =0) OR  (System.PlatformID = @PlatformID) OR (@PlatformID = 12 AND System.PlatformID &lt;= 2))  

REPLACE(@PivotColumnHeaders, *datecolumn*, *datecolumn* + '' '' + username + '' '' + CONVERT(nvarchar(10), recorded))