Using the information on skirts put together by David on his excellent site tiger1.info, we can recognise that this 504 gallery unknown has skirts of more than one pattern.
The skirts are fitted in a straight line, as introduced with the 3rd pattern. The rear three skirts are all the same length, confirming the 3rd pattern. The front skirt is different. It is made from two sheets of metal and overlaps skirt two, meaning it is longer than the others.
Skirts from the first pattern followed the bottom edge of the sponson hence the associated 'kink', the position of which resulted in the two rear skirts being longer than the front two. So here we see a rear skirt salvaged from a member of s.Pz.Abt.501, fitted in the front position on a member of s.Pz.Abt.504.