With 3dgs you have 4 lod stages!
I have the same models from Dex Soft, with 3dgs you can use only 4 of them. For example you can use the modells 0,1,2,4
I have a sample scene with house_0 in a far distance and the Debug panel visible.
The panel shows 10k tris from that distance.
If I move the camera away from that scene the tri number changes to 6k which is my _3.mdl
Going backwards until the model disappears behind the clipping range of the current camera, it still shows 6k until it switchs to 1k.
This means that the model is invisible due to the clipping range, but it is still in the debug panel - and strange enough, even the 5th LOD stage will be used even if it is invisible.
This seems to be a bug, because there is no need to throw 6k polygons against the gfx card if they are outside the view frustum.
[Edit]
Btw. have you tried shaders with those models? The shader viewer crashes with the big house model