It refers to a Tenshu which surely existed in the past but was afterward lost by fire, natural disaster, knockdown, or war damage and was reconstructed at the original location but with assumptive part in scale and design due to an intention not to be based on the historical facts and due to lack of historical data.
かつて存在したことは確かであるが、その後、火事・天災・破却・戦災で消失した天守を元の場所に、あえて史実に基づかなかったり、史料不足により規模や意匠に推定の部分があるものをいう。