Why does `ls -l` command show the year for some files' timestamp?

Issue

• Why does ls -l command show the year for some files' timestamp?
• The timestamp of old files show the year but others don't. Why?

$ date
Thu Feb 21 18:23:42 JST 2019
$ ls -l
-rw-r--r--. 1 user1 user1      408 Mar 16  2018 tool.txt
-rwxr-xr-x. 1 user1 user1      130 Feb  4 21:15 unind.txt
-rw-r--r--. 1 user1 user1       12 Feb  4 21:01 unindex.txt
-rw-r--r--. 1 user1 user1      343 Oct 25 16:18 user.ldif