It appears most blades were never used!
Antique 3 piece Carving Set, bone handles, sharpener, Carving Knife & Fork
Precision Hobby Knife Set with 3 Handles and 13 Blades - X-Acto Style
Tools -- The X-acto Knife
VINTAGE X-ACTO 3 KNIFE & 13 Blades WOOD CARVING SET IN Fitted WOOD BOX COMPLETE
Knife & Tool Sets @ Raw Materials Art Supplies
X-ACTO Compression Basic Knife Set, 3 Knives, 13 Blades, Soft Carry Case, 17 Count & X-ACTO 11 Classic Fine Point Replacement Blades, 40 Count : Arts, Crafts & Sewing
Making a 15/16th century moulded knife sheath - Sheaths and Leatherwork - Bladesmith's Forum Board
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.
Excel Carving Hobby Knife Blades —
VINTAGE X-ACTO 3 KNIFE & 13 Blades WOOD CARVING SET IN Fitted WOOD BOX COMPLETE