Continuous "load while run" printing of ordered sets of plural different sheets in a defined order in a printer paper path is provided even where plural different sheet feeding trays are stacked with multiple such ordered sets, by additionally loading therein near the bottom of the stack in between said ordered sets a control sheet with optically detectable control indicia which is detected in a printer paper path as that control sheet fed out from a first substantially but not fully emptied sheet feeding tray. In response to that control sheet detection, the sheet feeding from that first sheet feeding tray is automatically stopped to allow the reloading of additional ordered sets therein, and sheet feeding of further said ordered sets is automatically started from a second sheet feeding tray provide said continuous printing of said ordered sets in said defined order.