The memorization of training data by neural networks raises pressing concerns
for privacy and security. Recent work has shown that, under certain conditions,
portions of the training set can be reconstructed directly from model
parameters. Some of these methods exploit implicit bias toward margin
maximization, suggesting that properties often regarded as beneficial for
generalization may actually compromise privacy. Yet despite striking empirical
demonstrations, the reliability of these attacks remains poorly understood and
lacks a solid theoretical foundation. In this work, we take a complementary
perspective: rather than designing stronger attacks, we analyze the inherent
weaknesses and limitations of existing reconstruction methods and identify
conditions under which they fail. We rigorously prove that, without
incorporating prior knowledge about the data, there exist infinitely many
alternative solutions that may lie arbitrarily far from the true training set,
rendering reconstruction fundamentally unreliable. Empirically, we further
demonstrate that exact duplication of training examples occurs only by chance.
Our results refine the theoretical understanding of when training set leakage
is possible and offer new insights into mitigating reconstruction attacks.
Remarkably, we demonstrate that networks trained more extensively, and
therefore satisfying implicit bias conditions more strongly -- are, in fact,
less susceptible to reconstruction attacks, reconciling privacy with the need
for strong generalization in this setting.