While flying coupled in SEL HDG, the HSI still displays left-right deviation and distance, either from the VOR-DME in Radio mode, or from the INS in NAV mode.
How can a pilot be so numb as to ignore the HSI deviation needles, while unintentionally flying in SEL HDG mode?
OTOH, being coupled to the INS with wrong initial longitude makes everything look absolutely normal once past the first waypoint, which may have occurred even before they were turned loose to own navigation by ATC. This also explains how they were late on their position reports over SW Alaska.
GB