public void assign(int epoch, long startOffset) {
        EpochEntry entry = new EpochEntry(epoch, startOffset);
        if (assign(entry)) {
            log.debug("Appended new epoch entry {}. Cache now contains {} entries.", entry, epochs.size());
            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