The logic behind the "There is 1 additional version" from apt list

Question

Trying to understand the seemingly inconsistent behavior of apt list in regards to different packages on my Xubuntu 20.04.

Let's consider the two packages, blueman and xterm, both installed,automatic, both having received some updates after initial installation:

$ apt list blueman
Listing... Done
blueman/focal-updates,focal-security,now 2.1.2-1ubuntu0.2 amd64 [installed,automatic]
N: There is 1 additional version. Please use the '-a' switch to see it
$ apt list blueman -a
Listing... Done
blueman/focal-updates,focal-security,now 2.1.2-1ubuntu0.2 amd64 [installed,automatic]
blueman/focal 2.1.2-1 amd64

$ apt list xterm
Listing... Done
xterm/focal-updates,focal-security,now 353-1ubuntu1.20.04.2 amd64 [installed,automatic]
xterm/focal-updates,focal-security 353-1ubuntu1.20.04.2 i386
$ apt list xterm -a
Listing... Done
xterm/focal-updates,focal-security,now 353-1ubuntu1.20.04.2 amd64 [installed,automatic]
xterm/focal 353-1ubuntu1 amd64

xterm/focal-updates,focal-security 353-1ubuntu1.20.04.2 i386
xterm/focal 353-1ubuntu1 i386

Thus, although xterm seems to have even more additional versions than blueman, the abovementioned suggestion note is only included for the latter, not the former.

Why?

Answer 1

This doesn’t really explain the logic, but the implementation of apt list only shows the notice if the following two conditions are met:

• there are more versions to show;
• and only one version was shown so far.

On your system, xterm is listed for two architectures, so it is displayed in two “versions” (the same version on two architectures) fails the second condition.