To be honest, I have not used this functions myself but Yes Christine you can enter as Y. These macro functions are specific to SNP which mainly use the order series KF.
I would suggest to try both of functions and let us know if they helps you.
If this information helps you, request you to close the thread following using below steps.
http://scn.sap.com/community/support/blog/2013/04/03/how-to-close-a-discussion-and-why
Thanks
Amol