Picture this: you update a package and it's full of bugs! For example:
https://bugzilla.opensuse.org/show_bug.cgi?id=1042090

So you want to roll back to the previous package version. You run `zypper
search -s MozillaThunderbird` to find out what the the old version was:


$ zypper search -s MozillaThunderbird
Loading repository data...
Reading installed packages...

S  | Name                                   | Type    | Version    | Arch   |
Repository           
---+----------------------------------------+---------+------------+--------+----------------------
i+ | MozillaThunderbird                     | package | 52.1.1-1.2 | x86_64 |
Main Repository (OSS)

$

Darn. Only the latest version is available. Now you can't do a rollback except
by searching on software.opensuse.com, which is a royal pain.


Zypper should always keep information about at least version n-1 for every
package to facilitate rollbacks.