The values of the last_hardened_lsn column is not actual log sequence numbers (LSNs). last_hardened_lsn is flush LSNs and indicates the start of the next block past the blocks that are already on disk. So any LSN < the value of last_hardened_lsn is on disk. LSN that are >= to this value are not flushed. Please refer to this doc which might be helpful.
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