:y+YY or :y-YY
where the black text (:y+ and :y-) are to be be used literally, and the YY represents the numerical offset running from 1 to 99. For example, the token [8mc001:y-1] will display the 1st month (January) of the year that precedes the date of the token (based on DayValue 8).
Usually the order in which the calculation is made is not important, but in cases where the order makes a difference, then the calculation of the month to be displayed is done first using the usual marker ( 001 in the above example) to obtain January of the token's year, and then 1 year is subtracted.
See also : Offset from Current Year (for year tokens).