HI Bandela,
As Adam replied- with Year and Month filter, you cannot get last year data. Same issue you will get for next month when you try with 2005 Dec and expect 2006 Jan data.
I would rather create a user prompt on YYYY-MM and try to play with that.
Also, instead of 3 queries to achieve required data, I would go with one query using between condition.
The between condition would work as Month(yyyy-MM) between promptmonth-1 and promptmonth+1.
Let us know your opinion.
-Dhyan