For the testing period, while the office still reads the Excel cards. Every visit worked in Territory Manager that is not on a card yet is added to it — the count row and the fill row, by part number. A visit already on the card is left alone. Nothing is uploaded, and nothing in Territory Manager changes.
Pick the folder your route cards live in once — your Dropbox folder, or a folder you make for them (the chooser has a New folder button). Territory Manager remembers it on this computer, and from then on Update my cards adds your visits to every card in it, in place. A card that is open in Excel is left alone and named; close it and press the button again.