In your example you presented is the item identifiable as a more modern part due to design or other differences? If not is the question based on the fact that the glass or metal is not 50 plus years old?
Every restorer makes choices during a build. They are influenced by time, availability and resources ($$$ and other things). Rarely do projects start with a car so complete and in such great condition they will not need any additional parts, other than the original parts they left the factory with, that they will not require something to get it to the level the owner wants a car. If so then normally these are left as is and referred to as unrestored or some other label.
We each make these choices and the challenge for some can be how they will describe the finished project since any label can be interpreted differently by different people. Bottom line for me at this point this is a difficult question to answer as it depends IMHO on a ton of things and would differ from project/car to project. Examples abound and discussing each will take up pages only to reach in the end, I believe, that it's a personal belief and no two of us will be exactly at the same point on everything
Hopefully we each make the best choices for us as well as the vehicle and we're honest with ourself about those choices.