I can't fathom this "tradition" at all. My father was uncouth and crass and still would *never* have lifted my skirt unless I was in immediate need of medical attention.
As for the display of the bloodied bedsheets... I have a story about that. When I was a small child, I went to a bridal shower hosted by my father's family, who were Polish, Latvian, and Russian. My mother needed to leave urgently, and I was left in the care of my paternal grandmother, playing quietly in a corner while the womenfolk cleaned up after the shower and talked honestly to the bride about married life. They advised her that her mother in law would come to breakfast the morning after the wedding and would probably find an excuse to go snooping around the newly married couple's bedroom looking for that bloodied sheet. My cousin was gently advised how to fake the appearance of blood on a bedsheet if she needed to, where a cut would go undetected by even the groom, and how much blood was considered "enough" as opposed to just plain "fake". And that could not have been earlier than 1980.