Just ask them. It's probably not a big deal to take in something that's 3 months old if it's been frozen. Write on the bag "Frozen at 5:50pm, 3/3/12" so that it's clear, and if you can find a pen that will hack it, later write "Thawed on 4/5/12" or whatever.

Give them the chart from Breastfeeding Naturally to stick on the fridge where it's stored, and then all your bases should be covered.