To know how to use these files, read

For each edition, only the most recent installer is stored here.

The release date is not part of the filename, but it is indicated at the
root of the ISO file as SLINT_DATE. You can check it like it e.g.:
  mount <file>.iso /mnt
  cat /mnt/SLINT_DATE
There is also a README:
You can then umount the ISO file:
  umount /mnt
      Name                     Last modified      Size  Description
[DIR] Parent Directory - [TXT] README.TXT 06-Feb-2014 22:37 492 [TXT] Restore_an_USB_stick.txt 11-Nov-2013 17:08 923 [ISO] slint-13.37.iso 23-Apr-2014 08:18 36M [TXT] slint-13.37.iso.md5 23-Apr-2014 08:18 50 [ISO] slint-14.0.iso 23-Apr-2014 08:21 47M [TXT] slint-14.0.iso.md5 23-Apr-2014 08:21 49 [ISO] slint-14.1.iso 23-Apr-2014 08:23 54M [TXT] slint-14.1.iso.md5 23-Apr-2014 08:23 49 [ISO] slint64-13.37.iso 23-Apr-2014 08:20 27M [TXT] slint64-13.37.iso.md5 23-Apr-2014 08:20 52 [ISO] slint64-14.0.iso 23-Apr-2014 08:22 36M [TXT] slint64-14.0.iso.md5 23-Apr-2014 08:22 51 [ISO] slint64-14.1.iso 23-Apr-2014 08:25 44M [TXT] slint64-14.1.iso.md5 23-Apr-2014 08:25 51