It is a huge amount data that could never be covered , Canmore actually ignores the vast majority of hill cairns and some genuine prehistoric examples may have slipped through the net , see below ,but they do tend to mention the possibles /more likely examples .

The cairns found on the bigger hills in those less hospitable areas where there has never been any evidence of settlement or monuments and little settled even in early modern period are likely to be exluded because they are unlikely and often the bigger cairns in those areas are known to have been built by the OS , walkers or the estate .

I think the reason the others are ignored is that the sheer volume of cairns , most of which are clearly markers ,found on nearly every hilltop are usually too insubstantial to be a burial and some of bigger examples are known to be relatively recent , this suggests something other than the cairn with cists found in Wales ,Cumbria and to a lesser extent in Scotland .

Each should be judged on it's merits and I agree that Beinn na Caillich is a prehistoric possible as is Mad Meg's on Creag Meagaidh see http://www.geograph.org.uk/photo/100577 , the latter isn't even mentioned on Canmore and both have folklore that only muddies the picture ,although mad meg isn't quite so unlikley as a Norwegian princess .