There is a way to most definitely know which scenes have been added in the new version.
When you receive the compressed file, only the images added in the new version are created in the game\image folder. (not the entire image extracted with UnRen)
I haven't checked if this is the case with the original file, I always get the compressed file.
I've been doing it this way since version 0.51, which is why I don't write down what scenes are added in new versions anymore.
I don't know if this is HRelease's intention, but I find it very convenient, because it allows me to know even small scenes.