What "loose ends"? Did a searcher just tell them that they skipped a portion of their assigned section? That answer makes no sense to me. It is not as though they did not do a thorough search before.
In any search over rugged terrain, there are areas where SAR personnel can say with certainty that there is nothing there. Imagine a soccer field with three inch grass, for instance. All it would take is one person to walk the area once to ascertain with a high level of probability that there was no child there.
And then there are areas where SAR personnel can say they did not see anything of interest but cannot absolutely rule it out. Imagine a gully with walls that are covered with brambles and too muddy to walk or crawl down. In such an area, the searchers might space themselves at three feet apart but due to a bump or log or some feature of terrain be forced as far as eight feet apart in a few areas. SAR might rate such terrain at 95% probability of no child being there, even with the assistance of SAR dogs. Part of being certified is learning to rate one's search of an area honestly, not wishfully.
It is up to the SAR coordinator to decide what level of certainty they are willing to accept for what areas. This decision includes local conditions, number of searchers available and a number of other factors. In this case, I'd imagine that the SAR coordinator would want a very high level of certainty for the areas within half a mile to a mile of the school but be willing to accept a slightly lower certainty for areas 5 miles from the school.
If the terrain in the second scenario were more than a mile from the school and only reachable via equally rugged terrain, investing the effort to get to 100% certainty might be viewed as not being a wise use of resources, considering how much more terrain needed to be covered. Particularly in the first few days of the search, when hopes were high of finding Kyron alive.
Finding one 50 pound child in a circle of land that has a five mile diameter means covering almost 20 square miles. If the circle of land involved had a ten mile diameter, that increases the area to close to eighty square miles. In news accounts, it was unclear to me if the five miles referred to was radius or diameter.
I think a fair comparison of the difficulty would be for me to say I may have hidden a single size 11 seed bead in a stranger's house and bet you to find it. Maybe it's there, maybe it isn't. Even after you had searched thoroughly once, I think you'd probably want to go back and try again before paying up on the bet.
Or maybe you wouldn't be silly enough to accept such a bet in the first place!
With time, conditions change. I think there is little realistic hope that Kyron is alive.
Disturbing observation below:
If Kyron died on 4 June, his body may not have been putting out much scent in that first ten days. The weather that spring up until that point had been cool and rainy, which keeps ground cool, particularly vegetated or wooded ground. Cool conditions slow down decomposition.
Sometimes SAR dogs can pass right by very fresh remains because some local trick of the air currents prevents the scent from spreading.
I've seen this myself watching field hunters train. A bird gets shot in plain sight, falls, dog goes right to the correct general area and then goes nuts casting because they cannot scent the bird and their eyesight is such that the bird is not noticeable. I've actually heard dogs grunt in surprise when they literally tripped over the bird because it was not spreading scent as usual.
The weather has now warmed up and the air currents, even in wooded areas, will have changed. The sorts of air pockets where a bird can fall and not be scented are most likely to occur under cool conditions and unlikely to occur during hot, humid conditions.
After six weeks, if there is a body out there, it is now putting out a lot of scent if it is on land. That means that if the body were originally in some tiny pocket that were overlooked, it is now more obvious.