What it really shows (which we already knew) is that Primary Radar is pretty much useless in identifying aircraft, especially after the fact, isn't designed to do so nor to find "missing" aircraft, and no one is watching it except for "threats". Commercial aircraft are not threats, and not bearing down on military installations or ships, so not of any military significance.
Perhaps look at Korean Air 007 - part of the reason it was shot down was because the Soviets believed the US were using the cover of regular air traffic to try run surveillance flights - when the flight deviated from course by accident they took this as being an incursion. A "threat" won't always be a nicely lit up formation of mach 2 paints heading directly for major military areas. That said, 1983 was a far more paranoid time but I would have expected an unresponsive aircraft flying on a non standard route should have raised some suspicions - possibly not a threat level, but at least a "what is going on here".