Query to filter records between dates

I have a few queries which are used to create reminder email on training which is due for renewal.



Some training required reminder 6 months before 2 year expiry. I use this in the criteria for the training date within query:



Between DateSerial(Year(Date()),Month(Date())-18,1) And DateSerial(Year(Date()),Month(Date())-17,0)



Some training required reminder 3 months before 1 year expiry. I use this in the criteria for the training date within query:



Between DateSerial(Year(Date()),Month(Date())-9,1) And DateSerial(Year(Date()),Month(Date())-8,0)



My problem is with training requiring reminder 6 months before 3 year expiry. Using this criteria:



Between DateSerial(Year(Date()),Month(Date())-30,1) And DateSerial(Year(Date()),Month(Date())-29,0)



Doesn't show any results (although there is training which was done 30months ago, expiring in 6 months time).



Changing the -30 (months) and -29 (months) in above down to -22 & -21 shows records as expected, but anything below -22/-21 doesn't show any records.



Any help would be appreciated. :D



Thanks



Steve

Query to filter records between dates