I was of the impression that these covered breast plates were typical of the early 15th cent., often being of two or more parts. I can't recall a source for any of this but the the globose nature of the the breast was standard in the late 14th and early 15th centuries. The Axe/polearm you mentioned I don't think is a polearm at all but rather a
hurlbat. That is a small, all metal throwing axe with multiple points. The deep relief on the
shield makes me suspect built up plaster on the underlying wood though i've never before heard of such and don't know what such plaster might weigh. I do expect the wood to be ply and believe that it would delaminate with such deep carving but lack any practical experience on the subject.