  We report on recently published experimental studies on spin sum rules,
namely the generalized Gerasimov-Drell-Hearn, Bjorken, Burkhardt-Cottingham,
Schwinger, and generalized spin polarizability sum rules. The data were taken
at Jefferson Lab in Halls A and B by experiments E97-110 and EG4, respectively.
They covered the very low $Q^2$ domain, down to $Q^2$$\simeq$0.02 GeV$^2$,
where Chiral Effective Field Theory ($\chi$EFT) predictions should be valid.
While some of the obervables agree with the state-of-the-art $\chi$EFT
predictions, others are in tensions, including the Longitudinal-Transverse
interference polarizability $\delta_{\rm LT}^n(Q^2)$ for which $\chi$EFT
prediction was expected to be robust. This suggests that $\chi$EFT does not yet
consistently describes nucleon spin observables, even in the very low $Q^2$
domain covered by the experiments.
