I think such marks show the exact location where an item was stored in a rack. This sword marked B over 21 was likely in a rack for "Company B" or even "Rack B" and was to be stored in the the 21st slot. If the man assigned to take the weapon from slot 21 left the unit, someone else was assigned to take the weapon from slot 21, and I don't think you can figure out which man was which at any particular time. Some regiments of 900 men had total membership of several thousands of men over that regiment's service in the War, and how could anyone know who was assigned spot 21 in Company B at any particular time?
I think of it as how a parking garage might have parking spaces with markings, and I might be assigned Floor B, parking space #21 this month, and next month when I quit, or got promoted, or started walking to work, or got killed on the job, some other person would be using space #21 on parking level B.
I believe that we find these type markings more often on items used by units that had stationary assignments, such as on a ship, or in a fort, rather than units that were on the move.