Sometime between 1989-91 they deleted a cover pin, going from the traditional four showing to three. But... an engineering change order was issued in the spring of 1993 for the cover pins on all smooth delrin LB7s to be increased from two to three in order to close up the open cover on the front edge of the cover scale. This included the ivory delrin knives, so look at the SC507scrims for the years with three or four pins.
Codger