I imagine that dies were typically used until either the order that a merchant or other customer had placed was filled, or demand for the token subsided, or the die itself broke. So long as the die lasted it might be used on many orders, for the same or, sometimes, for different customers. It appears that after some period of time in the mid-1830's the Canadian banks stopped accepting the Tiffin tokens as currency and would only take them as scrap metal. This would pretty much effectively eliminate the demand. Consequently, as was not uncommon for some of the less sophisticated coiners, the die pair was put aside in a poorly controlled environment without the protection of grease or heavy protective oil to await another day when its services might be required.
Time passes, perhaps two or three years go by.
Or perhaps some old customer comes around to order more tokens as he had in the past, but at a heavier weight so as to compete with contemporary tokens more effectively. The lack of grease when the dies were set aside for storage and the humidity in the atmosphere have gone to work on the die steel and eaten and etched their way into the surface of the metal causing pitting and loss of detail. Some of the design comes off also, because, as our coiner polishes the surface of the die metal away to remove the rust, he also inadvertently removes some of the design details. Perhaps some of the lighter, more delicately engraved elements are polished off, perhaps some of the finer details are eroded entirely by the layer of rust. Either way, after he's done, our coiner decides it's time to touch the die up a little bit with some re-engraving to try to restore some of the lost details.