I think the idea of Moral shift is more nuanced though. Sometimes there isn't a shift in principle, but only in application. It is the big difference in the West, that an absolute Moral Law that we imperfectly approach was the tradition view, which some have come to consider morality only a construct since the 19th century. There is thus a difference between Relativists and Moral absolutists (though the latter necessarily imperfectly applied). For the Relativists, moral change represent real change, as morality is itself merely an abstract construction.
So for instance, everyone agrees killing is wrong. How we excuse certain instances thereof is the question. To the absolutist moralist, that support capital punishment say, we need to argue that Justice as moral principle supercedes killing being wrong; or if supporting abortion, that the foetus does not yet constitute a person. For a relativist, killing is just societal, so we essentially argue something constitutes an immoral act of murder only if not acceptable to society. It is the difference between humans deciding what is moral ourselves by consensus vs discovering a greater underlying principle, be that Religious or not in origin. Another good example is slavery, where the Church has always considered it immoral in principle, though inevitable in practice initially due to its universality - it was seen as a symptom of the Fall. The moral shift from the Abolitionists was not the change in the principle, but in the application that the institution could be tolerated as such.
The moral relativists, like Hume or Voltaire, argued slavery justified on grounds of cultural superiority or such, or Communists on the grounds of Utilitarianism.
The same with modesty. Most agree that people should dress modestly, but disagree how this principle should act in practice - a modestly dressed Victorian and Modern are far apart, but both agree to the principle and aim thereof. This is in contrast to supporters of Burlesque or so, who feel that modesty isn't a worthwhile thing, argue it constraining, and then point to other principles like individual freedom to support their contention.
Sufficed to say, there are two camps - One where the application of Morality differs, but the underlying principles are quite stable and coherent throughout; the other where societal consensus determines 'morality', and where dramatic shifts can occur quite suddenly, and in direct opposition to previous ideas (noted example Feminism and Transgenderism, which are frankly supposed to be directly at odds, idealogically).
