Your expression for the variable is correct, so there is no need to change anything there. The values of vYear_current in the list box were not produced by that expression as they are dates, whereas the expression returns just the year number.
There is some confusion though - you cannot show a variable (which has a single value) in a list box. So it seems you have a variable vYear_current AND a field named vYear_current and the list box is displaying the field values. There is no relationship between the variable vYear_current and the field vYear_current.
Logic will get you from a to b. Imagination will take you everywhere. - A Einstein
