蝦夷方言藻汐草

Batchelor explicitly gives Raokuru for a hidden rock, matching 沈み磯 and the full recorded kana. Hirayama cites that comparison, so it is not a second independent attestation. Retain the final vowel in raokuru; the shortened raokur remains an unconfirmed alternative. Both corpus queries return zero, which does not overturn the dictionary evidence or establish an eighteenth-century date for it.