public void assign(List<EpochEntry> entries) {
        entries.forEach(entry -> {
            if (assign(entry)) {
                log.debug("Appended new epoch entry {}. Cache now contains {} entries.", entry, epochs.size());
            }
        });
        if (!entries.isEmpty()) writeToFile();
    }
Assigns the supplied Leader Epoch to the supplied Offset
Once the epoch is assigned it cannot be reassigned
storage/src/main/java/org/apache/kafka/storage/internals/epoch/LeaderEpochFileCache.java