Most RC papers are not DI.

The "easy" way to ascertain this is to try lith printing - any DI will turn the image black immidiately as well as ruin the developer. This hasn't happened to me yet, although many RC papers simply fail to develop. Varycon has the same emulsion in RC and FB, as do MACO and Forte. I haven't tried others, although I can confirm that Ilford MG IV RC is one of the papers which simply don't develop.