Any milk that is still partially frozen will likely be ok if you re-freeze it ASAP. Any fully thawed milk will probably also be ok if you re-freeze it ASAP as long as it has been fully thawed for less than 24 hours. Any milk that has been fully thawed for more than 24 hours is questionable. But if it is close you can mark the bags with a permanent marker, re-freeze it and then give it the Kellymom Sniff/Taste test on a bag by bag basis.
I found a MilkShare posting with an opinion on this topic from David S. Newburg, Ph.D., Director, Program in Glycobiology, Pediatric Gastroenterology & Nutrition, Massachusetts General Hospital.
"My opinion is that if they are only partially thawed, there should be very little if any change to the milk upon refreezing, and that it will be fine for consumption."
Additionally, I have some other references that help explain why partially frozen milk should still be ok. The first link is to the Kellymom Guidelines (for healthy full-term babies, there are different guidelines for Preemies). As with most guidelines, it says you shouldn't re-freeze thawed breastmilk, without commenting on fully versus partially thawed. These guidelines are pretty widely accepted and comparable to any other reliable guidelines that I've seen.
However, these guidelines do mention the sniff/taste test (in general, not specifying refrigerated or frozen). Keep in mind that frozen milk can smell and possibly taste a little "off" anyway, so comparing it to fresh or refrigerated milk may mean throwing away milk that you might not need to; but unless you are familiar with what your frozen milk usually smells and tastes like you might want to err on the side of caution. On the other hand if it doesn't seem too bad you might take a calculated risk and try giving a small amount to baby --who is more familiar with it-- and see if he balks.
***The second link is to a recent Mothering article that implies that you can re-freeze fully thawed milk.***
The third link is to an article on food storage in general. The rule of thumb it gives is that you can re-freeze most anything that hasn't fully thawed.
I think the new rule of thumb combines the principles from the second two links. So it would seem that it is ok to re-freeze milk that hasn't fully thawed.
Breastmilk Storage & Handlinghttp://www.kellymom.com/bf/pumping/milkstorage.html
Traveling With Breastmilkhttp://www.mothering.com/articles/ne...reastmilk.html
“The researchers took frozen breastmilk and thawed it, refroze it, refrigerated it and left it out at room temperature. Essentially, they beat it up. What did they find? Breastmilk is fairly robust and does not grow bacteria easily nor lose vitamins A and C or free fatty acids (FFA) to any degree that would harm a full term baby.”
Quality for Keeps: Freezer Problem Solverhttp://extension.missouri.edu/explor...nut/gh1506.htm
EXCERPT "Refreezing: In general, food can safely be refrozen only if it still contains ice crystals or if it has been at refrigerator temperature (40 degrees Fahrenheit) for no longer than two days. In addition, use the following guidelines: If foods are completely thawed and have warmed above room temperature, foods should not be refrozen. Discard these foods. …”