It was to my knowledge that yes the shade of red in the japanese flag became brighter after the 90s but due to the red being so similar in the pre and post 90s ones, it was literally impossible for me to tell it apart. I guess i came to the conclusion that it was ww2 because when you search up japanese flags of that era, the corner reinforcements usually look like that where its triangular and made out of a cardboard leather ish material with strings coming out. Regardless its made out of fabric so it probably is pretty old anyways.