Is it necessary to repeat the ritual bath (ghusl) if an error occurred in specifying the intention for ghusl from janabah (major ritual impurity), such that the intention was for a specific janabah, but it later became clear that it was another janabah that was not intended? And what is the ruling if the error resulted from ignorance or inattentiveness until after the ghusl?

The intention for ghusl must be to remove major ritual impurity (hadath al-akbar) or to permit acts that are not permissible without ritual purity, such as prayer. It is not necessary to specify janabah (state of ritual impurity due to sexual activity). So, if you intend to remove major ritual impurity, or to remove janabah, or to perform ghusl for prayer, your ghusl is valid and your impurity is removed.