The title of your thread asks about Validation but your question asks about product realization.
With respect to Validation, 13485 only asks you to validate processes where the resulting output cannot be verified by subsequent monitoring or measuring. So with this understanding you need only assure that a process that cannot be inspected is proven to produce acceptable results.
This is like a sulfur analysis. Sulfur analysis requires that the sample be destroyed as a part of the process. In order to assure that the equipment that is used to perform the analysis is giving accurate results it is common to analyze a sample of material that has a known sulfur level. then analyze the unknown sample and then to follow up with another anlysis of the known sample. If the first and last tests are accurate it is reasonable to assume that the test on the unknown is accurate.
Validation is defined by ISO as: "Confirmation through the provision of objective evidence that the requirements for a specific intended use have been fulfilled."
Validation of processes performed by a Contract Manufacturer for Medical Device clients is generally understood to mean that prior to production and whenever you make any change to the process or equipment you will ensure that your processes, and equipment are producing products in accordance with the design specifications. If you run two shifts you will ensure that each shift is in compliance. If you change machines, machine speeds, dies, suppliers etc. you will run a proccess/equipment validation again before you resume production.
We have experienced inferior products from suppliers that have moved a process from type of machine that produced good product to another faster machine that they didn't validate. Once validated they discovered that the second machine introduced an error into the process that they weren't inspecting.
All of this must be documented.