In the "real world" it is a matter of your understanding with whomever you are providing the designs to. I don't know that there is any generally accepted practice. I'm sure it depends on whether your client is adequately knowledgeable about SketchUp. It also depends on the form in which your user expects to receive the model. You may have to convert it to something else, such as stl, before you send it on. In that case is it your problem to decide how your objects were meant.
Unless you annotate the model or provide separate documentation of your intent, someone using the model will have to provide their own interpretation. As noted, for some cases you can protect yourself by modeling at finer granularity (smaller Edges) than you know the user will require. Of course, this causes the model to have a very high Entity count.
You are faced with a fundamental aspect of SketchUp's design: it might be termed WYSIAYG (what you see is all you've got). In some other applications, an object is defined in an abstract mathematical form (e.g. center location, normal vector, and radius for a 3D circle) and is converted to line segments when and as needed. For instance, when rendered to the display, a circle needs to be converted to a raster image with pixels appropriate to the resolution of the display. On a different display, a different raster representation will be generated.
In SketchUp, there is no such higher-order abstract model. The Edges and Faces representing a shape are all there is. OK - picky point - a sequence of Edges can be joined together to form a polyline or polygon, but there is still no abstract model of the polygon as such.
So, for a circle, a user needs to know how to find the center and measure from there to a vertex to discover the original as-drawn radius. If it really matters and they don't have the SketchUp expertise to do this, you will have to do it for them and annotate the model.
This whole thing is a fundamental aspect of SketchUp's internal design, and part of how it obtains its much-treasured interactive user interface. Changing to the abstract-model-rendered-when-needed paradigm would be an end-to-end redesign of all the basic mechanisms of SketchUp.
Steve
