I work in big pharma.
I am unaware of the specific cases you may be referring to, but whether a component is already tested or not, is only a part of that process. Companies have to prove that a) they make that component exactly as described in the filing, and b) that the result is that particular component. Nothing more, nothing less.
For example, if I make aspirin, I have to make a filing with the FDA, with all the details of what I am going to make, en with an exact description of the process I am going to use, even going so far as dimensions of vessels, mixers, etc. the company I work for makes a specific drug that used to require being made in a 1000 liter reactor. We had to refile for approval for our 2000 liter bioreactors. And this was not simply a matter of rubber stamping. It started with a new audit, investigation, approval process etc.
Even moving a production line to a new plant next door means starting over. When we built our new plant right next to the old one, it took years to get approval. That is just how the regulatory process works. Not just the FDA in the US, but also the FAGG in Europe for example.
From breaking ground for a new plant to getting approval to distribute is a process that can easily take between 5 and 7 years. And this is because there is the need for guarantees on the process and the product, and not just 'best effort' or 'good enough'
Also, one of the additional requirements is that a company needs to prove they have all the organizational processes in place to comply with how a pharma company needs to be run. There is a thing called pharamcopeia which describes all the testing you need to have in place, how to deal with test results, how results need to be escalated, etc. You need to have working processes for dealing with exceptions and deviations, batch review and release, etc.
The product we make can be made by a PHd student with access to a simple million dollar lab. But to make a product that is suitable for intravenous use in compliance with ALL standards, takes a site with about 400 employees, half a billion dollar in initial investment, and ten to 30 million in annual upkeep costs.
Just saying: getting approval for actual use is orders of magnitude more difficult and time consuming than just making the component in a lab.