Is it sufficient for the sin to be forgiven, with intense remorse, to inform the owners of the bread that was taken without their knowledge of its value years later, with their acknowledgement and relinquishment?

If the bread is something that is not forgiven among friends, then you are absolved of its responsibility by regretting the act and by paying its value to its owners, because regret is repentance. Not explicitly stating that what you did was theft is correct, because concealing one's own faults is more preferable than exposing them.