RubberSouland here's an easier/foolproof way to know lipslide: it means you spin away from the rail, whether that spin is just 90, 270, or whatever
The only confusing thing about this is that, personally, I think of spin direction in relation to my tips. So when I think of sw lip, I still feel like I'm spinning "towards" the rail, because that's what my tips are doing. For example, approaching a rail switch, with the rail off my right shoulder, I would spin right and thus "towards" the rail. It's just a matter of forgetting that riding switch means my tails are acting as tips w/r/t spin direction, I think.
And also it's a moot point, cause no matter how you define what direction the spin is, the trick is the same. Phew, anyway, starting to make my brain hurt thinking about this.