Is it obligatory to make up for previous ghusls due to doubt about water reaching all parts of the body, and is ghusl valid with the intention of lifting old janabah?

A subsequent ghusl for janaba (major ritual impurity) removes all previous janaba, and there is no need to intend each individual impurity separately. Rather, the intention for janaba is sufficient to achieve complete purification. A doubtful hadath (minor ritual impurity) does not necessitate ghusl, and the default is that the previous ghusl was valid, because doubt after completing an act of worship does not affect its validity. One must abandon obsessive thoughts and not pay attention to them.