What is the difference between yum updateinfo list available/all?

Hello folks,

I'm somewhat confused about the difference in the following to commands. From yum(8):

updateinfo
[...]
yum updateinfo list [all | available | installed | updates]
[...]
which all display information about the available update infor-
mation relevant to your machine (including anything installed, if you supply "all").
[...]
* available Is used to display information about advisories for
packages available for updating or installation.
* all Is used to display information about both installed and
available advisories.

So

available

all

But the two opitions show different results:

# yum updateinfo list available | wc -l
19148
# yum updateinfo list all | wc -l
20473

Could someone explain the difference between the to options to me, please?

Regards,
Joerg