  Small uncertainties obtained for the Neutron Standards have been associated
with possible missing correlations in the input data, with an incomplete
uncertainty budget of the employed experimental database or with unrecognized
uncertainty sources common to many measurements. While further detailed studies
may improve the first two issues, the issue of potential unrecognized
uncertainties and correlations between different experiments has long been
neglected. We address this gap with a test-case study ons the evaluation of the
total neutron multiplicity of the $^{252}$Cf(sf) source, which is included in
the evaluation of the Thermal Neutron Constants within the Neutron Standards.
