The oddity is that I do not often find the Lyophyllum species you list, and come across the very rare ones just as often. I suspect the truth is that these 'rare' ones are not really so rare, but identification requires a microscope, and literature, and few people have both. So no doubt a lot of potential records are lost. A similar example is Melanotus horizontalis, which is supposed to be rather rare, but I come across it from time to time, mainly in Winter months.
Oh well, looks like the literature for this genus is a bit thin on the ground.