The subsequent investigation revealed that Shokakudo No. 1 Kofun Tumulus consisted of three overlapping round barrows with each of them having been built in different times whereby it became apparent that it was not a keyhole-shaped tumulus.
その後の調査により、松鶴洞一号墳は築成時期の異なる3基の円墳が重なり合ったものであり、前方後円墳ではないことが明らかになった。