the etext year.

http://www.ibiblio.org/gutenberg/etext06

(Or /etext 05, 04, 03, 02, 01, 00, 99,
98, 97, 96, 95, 94, 93, 92, 92, 91 or 90)

EBooks posted since November 2003, with etext numbers OVER #10000, are
filed in a different way. The year of a release date is no longer part
of the directory path. The path is based on the etext number (which is
identical to the filename). The path to the file is made up of single
digits corresponding to all but the last digit in the filename. For
example an eBook of filename 10234 would be found at:

http://www.gutenberg.net/1/0/2/3/10234

or filename 24689 would be found at:
http://www.gutenberg.net/2/4/6/8/24689

An alternative method of locating eBooks:
http://www.gutenberg.net/GUTINDEX.ALL