The HF23 didn't make a copy of the blockchain to create a new one, only made a change of the code to allow the thief of the funds. The technical analysis in blockchain terms is mostly irrelevant on the case and should be avoided to not confuse to the judge. The HIVE case and STEEM case are completely different in law terms, because in one you are retiring their funds from some accounts while in the other case HIVE didn't retired any funds of Justin's account but made a copy of the blockchain where those funds went to the DAO.
While for a programmer could be argumented that part of the DAO are stolen funds (which i don't think) for a court that should be simply ridiculous (as for the most people who understand the blockchain).
You can say HF23 is a hardfork and therefore a new blockchain but the fact is that is only an update of the blockchain.