U dont have R12 i the qvw, you need to chage the dimension to a combined Year&Month ( ex. 2015-08 ) i the Master calender. If u dont have a Master Calender i highly recument creating one.
Give the Attached file a look. in the file u fine different sulutions to R12, YTD, MTD
The expression also work just fine in Qlik Sense.
Calender set analysis.qvw 3.3 MB