Appending dataset where value labels differ across variables

I am attempting to create a longitudinal dataset from multiple survey files. My problem is for some of the variables the value labels are not the same across files, and so if I append only the value labels of the master file is maintained. I am not sure this is clear so let me illustrate with an example.

Say we have two files, file1 and file2, with same variable named var1 but different value labels as follows:


File1 File2

var1 var1
1 "2006" 1 "2004"
2 "2007" 2 "2005"
3 "2008" 3 "2009"

So, I have same variable but different value labels. If I append one of the value labels is dropped. Is there a way to convert the value labels to just labels? Say convert 1 "2006" and 1 "2004" to just 2006 and 2004 respectively.

Thanks in advance