Some blades are pretty close in overall blade outline, so RMK would occasionally put different models of knives and sheaths together as a means of expediency. 4 1/2" Model 4 was a standard size (no longer) available in 1957, so a model 7- 4 1/2" sheath fits. No need to have basically the same sheath made simply to have the "correct" model number stamped on it.