It appears most blades were never used!
Why You Should Buy a Marking Knife
My first proper little machining project made during my free time in my university's machine shop, a brass x-acto knife handle. Thoughts? I'm stoked with it. : r/Machinists
VINTAGE X-ACTO 3 KNIFE & 13 Blades WOOD CARVING SET IN Fitted WOOD BOX COMPLETE
Vintage X-Acto Craft Carving Tool Set in Original Wood Box - Not Complete
Vintage X Acto
Tools -- The X-acto Knife
VINTAGE X-ACTO KNIFE Set With Wooden Case 13 Piece Set $15.96 - PicClick
X-ACTO Products - X-ACTO - Knife Set, 3 Knives, 10 Blades, Carrying Case - Sold As 1 Each - Three styles with assorted blades that fit all three knives.
Precision Hobby Knife Set with 3 Handles and 13 Blades - X-Acto Style