What do you mean when you say they are both used in the module?
Do you have "current year" and "previous year" line items?
If you are using a list to represent time, these line items being list formatted, you would need an IF statement to check if your list item matched the "previous year" item and then pull the data from "current Year".
You should be considering using native Time though where functions like PREVIOUS() can quickly reference periods, in this case dimensioned by Years.