and unusual yes. people do weird things
For instance: removing a tail light baffle, replacing an oil pressure switch with a sheet metal screw, using a grease zerk for a brake bleeder, not tightening oil pan bolts, adjusting valve clearance to zero, advancing timing to 17*btdc, cutting wires to the trailer brake hitch, and destroying (but not fixing) the rear brakes by towing with the E-brake on.
All of those things have been done to my truck, and it would not surprise me in the least to find random parts missing. See why I'm a little nervous about what might be inside my engine?