I seriously doubt that malto is bad after 12 months of "optimal" storage. In fact my maltodextrin that I use for homebrewing is 4 years old and hasn't killed me yet. I think this is more of a "best by" date that the manufacturer adds to encourage you to use it up quickly. This is sugar after all, it should be nonperishable.
EDIT: They seem to attach the 1 year shelf life to all their products including steel cut oats. Sorry but that is pure BS. Brewers are fine using whole grains which are 2 years old and can still brew award winning beers from them.