I have an assembly to document which has an accessory power outlet, but I can only find the 2-pin and 3-pin Euro outlets. I seem to remember that there was a symbol for a North American style outlet at one time? Or was that in another CAD application?
Symbols don’t get removed just because of part obsolescence and the symbol libraries are tiny compared to 3D models, so no pressure to drop them.
Symbols/Footprints/3D models can get added/removed/reorganized at times. When that happens, you might not be able to find a particular part in the previous place it used to be available. If you have a design that used the old symbol, and if it is missing now, you can simply save it as a new symbol. This is possible because symbols and footprints are cached in the design files themselves.
When I migrated from 7.x to 8.x, my workflow was save as v8.x, validate, fix, save updated file.
There were a few symbols that looked like they ‘fell out’ during the conversion of the library to the updated format. I did capture a few and moved them to my libraries, including one that looks like a side view of a North American outlet (which I ended up using).