The way Im talking is reverse order full 3d clipping then projection - so maybe this way is a harder one but i do not see still the reason why it may be strictly incorrect (as I said it do not makes cuts of the figures in visible space that may occur in the first way (though anyway im not sure if this cutting effect my be masked so player will never see this or this makes visible artifacts though)
It's incorrect because you can end up with a triangle that contains a vertex at the tip of the pyramid, which is a degenerate point. The tip of the pyramid is technically on the projection line of every single point in space. The reason for a near plane is to avoid that problem.
this is not any problem though - if so you just can treat that whole screen is in the color of this point of the triangle