When styling an Impress multi-level list, there does not seem the be an option to also include previous-level numbers ("Show sublevels" in the Writer dialog), i.e. to have this: 1. Foo 1.1. Bar 1.2. Baz 2. Quux rather than 1. Foo 1. Bar 2. Baz 2. Quux which is the best we can do right now.
Valid request. The needed attribute 'text:display-levels' exists in ODF for number and outline lists.