From Tznius book:
“All women and girls must cover all parts of their body which Chazal have classified as Ervah. These parts include: the main body (torso), including the hip area; the upper arms, including the elbows; and the upper legs, including the thighs and knees. Their status of Ervah has been established by Chazal and is not dependent on the custom of the local women. . .
The hair of a married woman must be covered with non-see-through material (Kesubos 72).”
If people didn’t do so years ago or don’t do so now because they didn’t know or don’t know that they were or are supposed to do so; no one is judging them, but that doesn’t make it alright to do.
There is no such thing as “Tznius-dig by the accepted standards of TODAY.” There is only Tznius-dig by the standards of the Torah and Chazal.
If someone didn’t keep Shabbos years ago because he was told that he would lose his job on Monday if he didn’t come to work on Shabbos; we don’t judge him, because we’re not “in his shoes.” But the action is still Chillul Shabbos.