Operating two wireless cars simultaniously
No such thing as a silly question. The addressing on the encoder-decoder pair ensures that data is not received by a decoder with a different address from the encoder. A typical application for this would be a "secure" garage door opener where you program the door opener and remote to have the same address.

This will not prevent RF interference from messing up the reception of one or both receivers if you use two transmitters on the same frequency simultaneously. Unfortunately the solution is to split the two radio channels onto different frequencies.