I have been playing around with a huge stack of different papers as well as a long list of developers for quite a while now.
Ilford MG IV RC is almost impossible to get a reaction from by changing developer, dilution or anything else.
This is NOT a result of the RC base, as some other RC papers (MACO Lith RC, Varycon PE RC) behave quite normally.
Nor is it a result of the emulsion, as the FB version DOES react. And Ilford claim it's the same emulsion.
I have no idea what they've done to it, but at least it produces very stable results...