Hun, that's really a matter for your judgement. As you suggest, milk won't go off right on the dot of 12 months, however it will deteriorate at some point. I'm not sure that the exact time it takes is known, and probably it varies on a number of things, however it is known from testing that the milk is fine for 12 months in a deep freeze. If the milk still seems fine to you at 13 months then the chances are that it still is. EBM is known for it's anitbacterial properties which help it to last a long time. However there could be a small risk that it's not, which is why the guidelines say 12 months. I'd say trust your own instinct on this one.

And I know what you mean about throwing it out. Broke my heart to throw out a freezer full of EBM when DS self-weaned