同類號又同作者號時，再區分方式有2種：
(1) 在作者號後 + 阿拉伯數字 或
(2) 在作者號後 + 英文字母

When two authors share the same number, it is advisable to add a digit. A good number to select is 5, as there is then room on both sides for additional interpolation as necessary.
A book already in the collection by Richard Colby would be C686. A new book to be added to the same classification number by another author named Colby would need a different author number. A book by Simeon Coby could then be C6865. This leaves room for the insertion of additional authors between Richard and Simeon ─ using C6862, C6863 and C6864.
上述原文摘自Cutter表中”How to use the Cutter-Sanborn Table”，係用阿拉伯數字的作法，第一位用C686, 第二位同號作者用C6865, 是預留2-4間的空號。當然也可以採用流水號1, 2, 3, …的方式。

國圖是用a, b, c,…. 的方式
如第一位作者C686, 第二位同索書號的作者用C686a, 如此類推。

錢月蓮敬答  20140419