Reefer Ice Hatch Locks

I am in charge of the D &RGW 30 ft Reefer restoration for the Durango Railroad Historical Society.
Note the attached pic of the Ice hatch lock on the Chama. it is an original lock that was left on the reefer- not added by the Chama group. You can see a small slot that was cut diagonally thru the slider locking pin. This was for a railroad seal to lock the car and make sure the car was not tampered with during perishible shipments.
For our restoration there are none to be had so we had to have four fabricated. Now we find out that the same locks were used on the D &RGW 3000 series boxcars end lumber doors EXCEPT THAT THE BOXCAR LOCKS HAVE NO SLOT IN THE LOCKING PIN.
Can anyone tell me why there was this difference? Same lock! Can it be because of the perishable nature of the merchandise carried in the reefers made it neccessary to protct the car better?
Big Steam