Hello,
If you want to use the current year, just use the formatDateTime() function.
Ex:
formatDateTime(addYears([%CurrentDateTime%], -1), 'yyyy')
You can use the formatDateTime to just get the year from a date as a String, and you can add -1 years to a date using addYears. Something like this should work.
formatDateTime(addYears([%CurrentDateTime%], -1), 'yyyy')