In the first half of Tenet, there is a scene where The Protagonist and Neil break into Freeport and find a glass wall with bullet holes (could only find a good photo with Christopher Nolan in it):
In the next scene, we find out that these bullet holes were caused by an inverted armed man entering the room (exiting the room from their perspective) and reverse-shooting the glass, which removes the bullet holes from the future-facing perspective. This all makes sense, but raises a question: how long were the bullet holes there in the first place? Were they in place as soon as the glass was installed, possibly years ago? Or even back when the glass was manufactured?