Use the following query

select @cols = STUFF((SELECT ',' + QUOTENAME(Date)

FROM #distinctDate

Order by [year], MonthNumber

FOR XML PATH(''), TYPE).value('.', 'NVARCHAR(MAX)'),1,1,''

)

I have remove the distinct, if you want to distinct the record to it when you create the #distinctDate

after that i have added the order by clause, because there is no such thing as Natural Order 😀