At many places in beta decay of cobalt-60, the ground state spin of the isotope is given as 5+. However that's not what is predicted by shell model and applying nordheim's strong rule. Is the data given purely experimental in such cases and outside purview of shell-model? Similarly, daughter nucleus Ni has 4+ spin-parity. Is there a theoretical way to determine the nuclear spins in ground state?
Shell Model arguments usually work well for nuclei close to magic neutron and proton numbers, but sometimes fail when that is not the case. Co-60 is just not magic enough. Here is a link to an old paper that might help: http://ist-socrates.berkeley.edu/~schwrtz/PhysicsPapers/01PhysRev_94_95.pdf The data in the nuclides chart is experiemntal and there is no theoretical model that explains all the measured gs spins, especially for the most challenging odd-odd isotopes.