What does the letter after a year mean eg 1923a or 1915e?

The letter after a year, such as in "1923a" or "1915e," typically denotes a specific edition or version of a document, publication, or artifact from that year. This system can help distinguish between different releases, revisions, or interpretations that may have occurred within the same year. For example, "1923a" might refer to the first edition or a particular variant, while "1923b" would indicate a subsequent version. This practice is commonly used in academic contexts, publishing, and cataloging to maintain clarity about the material's provenance.