Here's a sentence from the "Critical Introduction to Law and Literature" by Kieran Dolin:
His decision denied that these indigenous peoples had proprietary rights to the lands in question, despite their continuous occupancy since before the coming of whites.
The meaning seems to be the same as "before," but I can't find proof in any dictionary. This phrase sounds very strange to me, as 'since' and 'before' are almost opposite, and here they are together.