There are three ways that you can use the MFG. YEAR in the DataRef system.
Selecting a range of years to stay within
This search is useful when you are looking for auction results that are within a few years of the manufacturing year of what you are looking for.
Finding All of the Machines that were Manufactured After a Certain Year
By leaving the Max year blank, you are asking for results that start at the year you specified and newer.
Finding All of the Machines that were Manufactured Before a Certain Year
By leaving the min year blank, you are asking for results on machinery that was manufactured before the specified max year.