Judy,
I am the coordinator of the milk bank/breastfeeding center in Worcester,
MA.  The guidelines  that we use are as follows:
If freezer is maintained at zero degrees fahrenheit in a freezer with a
refrigerator milk can be stored for 3-4 months easily.
If milk is stored at zero degrees in a non frost free separate (no
refrigerator) freezer it can be kept for one year.
Darlene Breed RN, BSN, IBCLC