Hermann von Soden published a complex cataloging system for manuscripts in 1902–10. He grouped the manuscripts based on content, assigning them a Greek prefix: δ for the complete New Testament, ε for the Gospels, and α for the remaining parts. This grouping was flawed because some manuscripts grouped in δ did not contain Revelation, and many manuscripts grouped in α contained either the general epistles or the Pauline epistles, but not both. After the Greek prefix, von Soden assigned a numeral that roughly corresponded to a date (for example δ1–δ49 were from before the 10th century, δ150–δ249 for the 11th century). This system proved to be problematic when manuscripts were re-dated, or when more manuscripts were discovered than the number of spaces allocated to a certain century.