Me earlier:
This constrains the possible dating systems in Jeremiah to Nisan/accession (starting from the year that began in Nisan of 609 BCE) or Tishri/non-accession for kings of Judah.
For clarification, those constraints are what is imposed by the placement of the battle of Carchemish. Examination of additional passages specifically identifies Tishri/non-accession dating as the correct dating method for kings of Judah in Jeremiah and 1&2 Kings. But that additional examination is not necessary for establishing 587 BCE as the correct year.