  We present a comprehensive impact study of future Electron-Ion Collider (EIC)
data for parity-conserving and parity-violating polarization asymmetries on
quark and gluon helicity distributions in the proton. The study, which is based
on the JAM Monte Carlo global QCD analysis framework, explores the role of the
extrapolation uncertainty and SU(3) flavor symmetry constraints in the
simulated double-spin asymmetry, $A_{LL}$, at small parton momentum fractions
$x$ and its effect on the extracted parton polarizations. We find that
different assumptions about $A_{LL}$ extrapolations and SU(3) symmetry can have
significant consequences for the integrated quark and gluon polarizations, for
polarized proton, deuteron and $^3$He beams. For the parity-violating
asymmetry, $A_{UL}$, we study the potential impact on the polarized strange
quark distribution with different extrapolations of $A_{UL}$, finding the
constraining power to be ultimately limited by the EIC machine luminosity.
