These are bars that are misshapen, didn't release from the mold well, cracked when getting stamped, accidentally got cut too small, or developed a lot of soda ash* on the surface.

*Soda ash (sodium carbonate) - A white powdery substance that can form on the outside of a bar of soap when the lye in the soap reacts with carbon dioxide in the air as it cools.  It is HARMLESS and does not affect the soap's effectiveness.