I want to be able to grab any copy of An Investigation of the Laws of Thought off a book shelf, read the physical ISBN off the back of the book, and have it match my inventory. Exactly what verification means can be a bit fuzzy. At one extreme, prison inmates have their fingerprints taken at control points when they are transported and courts allow DNA evidence for convictions. At the other end of the spectrum, retail stores will accept your check on the assumption that you look like your driver's license photograph. This is fairly easy to understand in the case of entities, which like people are obviously unique.
Nobody puts a part number on the grains of rice in a bag.
The English language makes a distinction that other languages do not. The distinction between a unique entity, a collection of indistinguishable units, and a divisible mass can shift. To pick an example from the literature, imagine that you are breeding laboratory rats. The ratlets are treated as a litter and assigned a litter number when they are born. As they grow up, each little rat becomes an individual and assigned a unique identification number, encoded in colored markers on his tail.