We leave the marking of edited text up to each member. It is entirely possible to mark up any alterations by italics, strike-through text etc., but this easily gets too complicated and error-prone.
If there is a significant change in the original text, and such parts have lead to later replies etc., I think adding a strike-through style to the paragraph(s) is in order, plus an Edit line at the end of the post stating why text needed a change. Nobody is infallible.
However, as stated in my first answer, the finite editing window is there for a reason.
