Why doesn't "getent passwd username" command show user's information if username is ALL numeric?

Issue

• Why doesn't getent passwd username command show user's information if username is ALL numeric?

• There are some numeric usernames in NIS server, on NIS client, 'getent passwd username' command doesn't work for ALL numeric usernames:

[root@rhel ~]# id 12345
uid=67890(12345) gid=10(wheel) groups=10(wheel)

[root@rhel ~]# ypcat passwd | grep 12345
12345:x:67890:10:Test Numeric User:/:/bin/bash

[root@rhel ~]# getent passwd | grep 12345
12345:x:67890:10:Test Numeric User:/:/bin/bash

[root@rhel ~]# getent passwd 12345         <---- Doesn't return any info
[root@rhel ~]# getent passwd -s nis 12345
[root@rhel ~]# echo $?
2