Hi,
Thank you for the clarification.
In this case, I suggest a different approach - you might build a sprint hierarchy by name.
You might find more details on that approach here - Aggregate Sprint By Name - #7 by zane.baranovska.
You would need to modify the JavaScript code to extract the Sprint name without board.
That might be something like the following.
 var sprintnum = null;
 if(sprint.name && sprint.name.match(/S\d+/)){
   sprintnum = sprint.name.match(/S\d+/)[0];}
   else {sprintnum = sprint.name;}
That would allow importing additional sprint property which could be used to create an additional sprint hierarchy.
That would relieve you from the manual creation of new calculated members for every new sprint cycle.
Regards,
Oskars / support@eazyBI.com