Ay, good question! Kapag nag-thaw na, look for any off smell or weird color, kung medyo yellow-ish na or may sour smell, discard na agad para safe lang. A few of us mums usually label our frozen stash with the date using masking tape, kaya alam agad natin kung ilang months na siya, at generally okay pa ang frozen breastmilk for up to 6 months depende sa freezer type mo (kaya importante talaga ang date marking!). If you're unsure, better safe than sorry, trust your gut at mag-throw away na lang rather than risk it with baby.