Hi, add one month to date can work?:
//Add previous month data to next month
LOAD Date(AddMonths(Date#(Datefield,'YYMMDD'),1),'YYYY-MM-DD') as Datefield,
Data as DataLastMonth
(biff, embedded labels, table is Sheet1);
You can add a 'Where' clause to limit to one month and also to not add rows "after AddMonths(Today(), -1)" to not create future data.
You can also do a group by to keep Data and DataLastMonth in one row per Datefield.