wget - N sempre refaz o arquivo mesmo se o timestemp não mudar

Question

Eu encontrei este site sobre como baixar arquivos, dos quais o timestamp mudou:

link

Eu testei, mas o wget sempre continua fazendo download novamente. Mas o registro de data e hora não muda. O que eu não consigo chegar aqui?

[tom@machine Downloads]$ ll
total 48536
-rw-r--r-- 1 tom students 49693179 Apr  5 07:22 assembly_summary_genbank.txt
[tom@machine Downloads]$ wget -N ftp://ftp.ncbi.nlm.nih.gov/genomes/genbank/assembly_summary_genbank.txt
--2018-04-05 18:24:42--  ftp://ftp.ncbi.nlm.nih.gov/genomes/genbank/assembly_summary_genbank.txt
           => ‘.listing’
Resolving ftp.ncbi.nlm.nih.gov (ftp.ncbi.nlm.nih.gov)... 165.112.9.229, 2607:f220:41e:250::11
Connecting to ftp.ncbi.nlm.nih.gov (ftp.ncbi.nlm.nih.gov)|165.112.9.229|:21... connected.
Logging in as anonymous ... Logged in!
==> SYST ... done.    ==> PWD ... done.
==> TYPE I ... done.  ==> CWD (1) /genomes/genbank ... done.
==> PASV ... done.    ==> LIST ... done.

.listing                                                 [ <=>                                                                                                                  ]   1.11K  --.-KB/s    in 0.002s  

2018-04-05 18:24:44 (449 KB/s) - ‘.listing’ saved [1133]

Removed ‘.listing’.
--2018-04-05 18:24:44--  ftp://ftp.ncbi.nlm.nih.gov/genomes/genbank/assembly_summary_genbank.txt
           => ‘assembly_summary_genbank.txt’
==> CWD not required.
==> SIZE assembly_summary_genbank.txt ... 49693179
==> PASV ... done.    ==> RETR assembly_summary_genbank.txt ... done.
Length: 49693179 (47M) (unauthoritative)

assembly_summary_genbank.txt                         100%[=====================================================================================================================>]  47.39M  5.44MB/s    in 9.1s    

2018-04-05 18:24:54 (5.20 MB/s) - ‘assembly_summary_genbank.txt’ saved [49693179]

[tom@machine Downloads]$ ll
total 48536
-rw-r--r-- 1 tom students 49693179 Apr  5 07:22 assembly_summary_genbank.txt