Hola!
A 'Selectable(Package,glibc)' will contain at most ONE installed, and all available glibc packages. ;(
There is no difference, unless more than one version of a package is installed. In that case there are as many Selectables as there are versions installed. Each Selectable links to only ONE installed but to ALL available versions.
Unfortunately we support this (e.g. multiple kernel versions being installed at the same time).
My apologies for the dumb question *), but if the concept of selectables has so many drawbacks, why did we decided to use it? Why didn't we switch to PoolItems instead? Can anyone (Michael, HuHa,...) comment on that in some human-readable, easy-to-understand way? ;-) Thanks B. (*) read: I've joined YaST team only a year ago, already after package management rewrite -- \\\\\ Katarina Machalkova \\\\\\\__o YaST developer __\\\\\\\'/_ & hedgehog painter