  A recent analysis of experimental data [J. Wilson $et. al$, Nature $\mathbf
590$, 566 (2021)] found that the angular momenta of nuclear fission fragments
are uncorrelated. Based on this finding, the authors concluded that the spins
are therefore determined only $after$ scission has occurred. We show here that
the nucleon-exchange mechanism, as implemented in the well-established
event-by-event fission model $\mathtt{FREYA}$, while agitating collective
rotational modes in which the two spins are highly correlated, nevertheless
leads to fragment spins that are largely uncorrelated. This fact invalidates
the reasoning of those authors. Furthermore, it was reported [J. Wilson $et.
al$, Nature $\mathbf 590$, 566 (2021)] that the mass dependence of the average
fragment spin has a sawtooth structure. We demonstrate that such a behavior
naturally emerges when shell and deformation effects are included in the
moments of inertia of the fragments at scission.
