What is the ruling on not washing the dirt from the glans of the penis during ghusl, due to ignorance of the ruling?

If the dirt on the glans of the penis does not prevent water from reaching the skin, then the ghusl (ritual bath) is valid and it is not obligatory to wash it off. However, if it does prevent water from reaching the skin, then the ghusl is not sufficient and it must be removed to ensure water covers the entire body. If the area that prevents water was not washed due to ignorance, then the prayers performed after that ghusl are invalid and must be repeated.