Breastmilk storage question

PhillyGal34

I have a LOT of frozen milk (as in at least 2000 ounces).  Right now my oldest milk is about 4 months old but it has been stored in a chest freezer at 0 degrees since it has been pumped.   I am trying to rotate my stash and freeze my fresh milk but I'm also giving a bit of the fresh milk while I am at work so he is getting more of my antibodies right now as we go into the cold/flu season.  I don't want to have a lot of wasted milk though.  My plan is to breastfeed until 14 months (one year adjusted) and then continue giving him milk until my freezer stash is gone (as long as the milk is still good of course). 

I see on kellymom that milk can be stored in there for up to a year but 6 months is ideal.  My question is what happens after 6 months that makes it less than ideal?

 

ETA- my son is a preemie but I've spoken with the lactation consultants and they said I can use the regular milk guidelines at this point.