I could be wrong, but I don’t think North Korea interred any remains properly.
Are the remains scattered over a hundred thousand acres having been picked apart by scavengers? The North Korean dictatorial government of the last 50 plus years has always been a tyrannically oppressive regime fed by the bloodlusts of demented meglomaniacs.
And we are looking for order among the chaos?
After chasing the North Koreans back across the 38th parallel, the Americans established defensive positions deep in North Korea. The positions were weak and thin. McArthurs generals disregaarded their intelligence and lost their troops.
When the Chinese attacked whole battalions were anniliated. During the retreat, the Chinese occupied positions on ridges on both sides of the only road for retreat. Thousands os US Army soldiers were killed. The retreat was one of the most costly blunders in American military history
Those places with thousands of American dead are the places where there are bodies that can be returned. Since there are so many, the probability of identifying and getting all of them returned is not very great