You would need to look at the source. However, if you known the WoT
well, you should be able to figure out what this is. For example at
depth 0, you see 8 ultimately trusted keys. At the next level you
obviously find no ultimately trusted keys but 20 marginal trusted and 1
fully trusted key. You should consider this a debugging output.
> gpg: next trustdb check due at 2013-12-31
The check run found that due to key or signature expiration a new trust
check is due on that date. It is informational only, because that date
is stored in the trustdb and a gpg --check-trustdb --batch before that
date will conclude that this time it can be lazy and exit immediately.
Die Gedanken sind frei. Ausnahmen regelt ein Bundesgesetz.