Thanks for your help. My problem is that I use brute force sometimes, and while that "works", it is not always the best solution nor the one that I really need. Here is what I have attempted:
SimpleMarkerOverlay pointOverlay = CurrentOverlays.PlottedMarkerOverlay;
Vertex v = proj4.ConvertToExternalProjection(lon, lat);
PointShape p = new PointShape(v);
Marker m = new Marker(p);
I've actually subclassed the Marker class and added some things to it, but that's another discussion and can wait until I get this issue addressed first.
In fact, I add several thousand markers at different locations before actually refreshing the Map, but that's not important either. What IS important, is that this layer is NOT included in the displayed Layer List, and I need it to be displayed there so that I can export the layer with its contents to a shapefile using the built in functions of the Editor.
After looking at some code in that web site, even though it doesn't directly answer my particular issue here, I am getting the feeling that I am missing quite a bit of prep for this layer that would make it recognizable to the system as a layer to be included in that list a suitable for export.
For example, I see the necessity for definition of column data, which I do not have here. I also see the DrawCore method for a pointstyle being overridden, and I am doing none of that, just including render information in my marker class. Clearly, I am not following the correct design pattern for the Editor to accept my data for inclusion into the Layer List.
Do you know of any SIMPLE examples that demonstrate how this can be done? Once I understand exactly what needs to be done, I can take it from there.