[michaelt]

As far as I know, CAs don't have to "save up to their latest entry"

The info they get back from the CT log may be a Merkle Hash that partly depends on the other entries in the log - but they don't have to store the entire log, just a short checksum.

[torbid]

Right and this is what I am saying is backwards with the protocol. It is not in anyone's best interest that some random 3rd party takes responsibility to preserve data for CAs indefinitely to prove things. The CA should identify where it has its copy in the extension and looking at one CAs copy one would find every other CAs copy of the same CT log.