RPI(s) and co-formulation

In case of a co-formulation with molecule 1 (which already has an RPI) and molecule 2 (no RPI yet), should we request an RPI for molecule 2 and use either RPI for any forthcoming submissions via IRIS? Or should we request an RPI for the co-formulated product (new RPI with molecules 1 and 2 referred)?

I assume that by "co-formulation" you mean a fixed-dose combination product (FDC). A FDC is a different product, therefore it needs its own RPI. If no product containing ONLY molecule 2 is being developed, then no RPI is needed for molecule 2. RPIs are assigned to track development entities, including potential or existing medicinal products, not to track substances.