You are wrong.
There was something about that in the oficial source.
You can use librarian on bike because there is No such unit in the codex, So you can use entry fron index And its valid.
But in the codex there is unit called dreadnought So it teplace the entry from the index.
I am not.
There are a few options that are missing in the codex that appear in the index: why is that? Does that mean I can’t use these models in my army anymore?
While the indexes are designed to cover a long history of miniatures, the codexes are designed to give you rules for the current Warhammer 40,000 range. There are a few options in the indexes for some Characters and vehicles that are no longer represented in the Citadel range – certain Dreadnought weapons that don’t come in the box, or some characters on bikes, for example.
Don’t worry though, you can still use all of these in your games if you have these older models. In these instances, use the datasheet from the index, and the most recent points published for that model and its weapons (currently, also in the index).
They still gain all the army wide-bonuses for things like Chapter Tactics and can use Space Marines Stratagems and the like, so such venerable heroes still fit right in with the rest of your army.
I hope that settles that debate once and for all.
If the model has the option in the Index, it's still valid now.