I agree...If you look at how a Production Red (Red sex link, Red Stars.. etc...) becomes, you will find that it really is only in it's purest form... 1/2 Rhode Island red. (And that is to say that the breeder even used a RIR, as they don't have to! It can be many gold gened roosters!)
But, there is much confusion about RIR's. When you start breeding out qualities that a RIR has, such as being dual purpose, to just one purpose, being egg laying, you have to go outside what the SOP states a RIR is and should be. (And outside those original lines) In short, when doing so, it isn't a RIR any-longer.
A True RIR bread with a true RIR will not be a production bird. It will be a True RIR that is a dual purpose egg-layer and meat bird.
Essentially, a Production Red is a cross breed. That is why you can not trace the lines, as you will most times not even know what is being used to produce a production layer. I mean you could, but you would only be tracing the one side.. and that is if it is even a RIR that is being usd, as there are quite a few combinations that will yield production reds. (Breeding wise)