I usually find difficult to keep track of which support library versions are available and is quite frustrating when I cannot find the exact number I need for a specific sample that I build months ago.
To this I can add that Android Studio always complain when I try to use something with a + in the version (to avoid to specify the full version)... this has been something bothering for me way too much:
Caution: Using dynamic dependencies (for example, palette-v7:23.0.+) can cause unexpected version updates and regression incompatibilities.
We recommend that you explicitly specify a library version (for example, palette-v7:25.4.0).
At the end I searched and found: Recent Support Library Revisions
This page provides details about the most recent Support Library package releases. For earlier releases, see the Support Library Revision Archive.
Finally!!!