It appears most blades were never used!
Tools -- The X-acto Knife
Vintage X Acto Knife Set FOR SALE! - PicClick
Curved blade with a handle hi-res stock photography and images - Alamy
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.
Utility knife - Wikipedia
Vintage X-Acto Knife Set With Wooden Case 13 Piece Set
Why You Should Buy a Marking Knife
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 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
Curved blade with a handle hi-res stock photography and images - Alamy
Vintage X Acto Knife Set FOR SALE! - PicClick
Exacto Blades at Jerry's Artarama