They do come in numbers, but they all mean different things for different manufactures. I believe an OS #8 is their standard medium-hot plug with their A3 being their standard hot plug.
I only use their LC4 plug now in my OS21TM one of my revo's, it uses a longer reach plug and I run 25% fuel, so I run a bit cooler plug. Seems to perform better for me. I use purple odonnel plugs in my LRP28 in my big block revo. They always ran good for me in that. That's their "medium" plug as well.
Do you have a photo of the plug you took out of yours?