I've been wondering about this per a unique business system I've been working on... Hypothetically, if you have a situation where you are not allowed to delete any prior business data (i.e. append-only event log), what would stop you from directly using prior log entries as the basis for some sort of incremental/recursive compression dictionary?

Put differently, is there any way to leverage scenarios where you have a practically-unlimited dictionary size and willingness to retain all data forever? Or, am I playing with some basic information theory equation the wrong way in my mind?