As shown in the example above, the problem arises if e.g.
Ana Horvat, who should be alphabetically the first author on the
shelf, arrives as the fourth author in the class. The only notation
available for her is HOR.A which places Ana after Ivan Horvat
who has already occupied the notation HOR. This problem with the
accuracy of the alphabetical order is the main disadvantage when
using letters instead of using author numbers.