Stamp #903-904 came together as a se-tenant pair. So did #905-906. These are wonderful stamps of Canada’s aviation history. I have a FDC of all 4 stamps (903-906) connected as a block. Since #903-904 came together, and #905-906 came together, how is this possible? Did Canada Post create a special “block” consisting of #903-906 just for the FDC issue? Insight is greatly appreciated.