They definitely can and do scrape Signal logs and use them in court. The protocol doesn’t help them prove the validity of the log, but they don’t need it to: it’s already not plausible to claim that you and your contact falsified your logs, something few people know how to do, in sync, in order to frame yourselves. I think Signal’s approach to deniability is just not making it even more hopeless, while the real protection against future compromise of a currently trusted contact or your own device lies in a different strategy that does work, ephemerality.