A fun thing about historical archaeology, the archaeological study of areas and periods with abundant indigenous written documentation, is when the archaeology challenges the written record.
According to the patchily preserved historical sources, Landsjö hamlet was a seat of the high nobility in about 1280 but then became tenant farms no later than 1340. This means that the castle on Landsjö islet was probably in good defensible shape and inhabited in 1280 but not after 1340.