Systematic uncertainty of offshell corrections and higher-twist contribution in DIS at large x

We study the systematic uncertainty and biases introduced by theoretical assumptions needed to include large-$x$ DIS data in a global QCD analysis. Working in the CTEQ-JLab framework, we focus on different implementations of higher-twist corrections to the nucleon structure functions and of offshell PDF deformations in deuteron targets and discuss how their interplay impacts the extraction of the $d$-quark PDF and the calculation of the neutron structure function at large $x$.