Apologies for the delay, I have been cloudflare'd out of the forums.
If you have multiple GRFs, you have to define multiple patch processes in the config as per the documentation.
So one section, ex. "[ROCred.Patchers.Main]", can be for your adata.grf and another one, ex. "[ROCred.Patchers.Event]", can be for your bdata.grf. There is no hard limit to the amount of GRFs.