There are some cases where slaves fail before getting far enough to ever update CIDB at all.

These cases can be detected via buildbucket.

Examples include:
1) Builders that are offline.
2) Builders that have no CIDB credentials.
3) Builds that fail in the build recipe or very early in cbuidlbot.

It could be nice to notice these cases and update CIDB to reflect what happened based on the buildbucket data. It might be appropriate do this this in a CIDB cleanup script such as has been proposed in crbug.com/707897.