Defect-driven ferrimagnetism and hidden magnetization in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mrow><mml:mi>MnBi</mml:mi></mml:mrow><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mrow><mml:mi>Te</mml:mi></mml:mrow><mml:mn>4</mml:mn></mml:msub></mml:math>

MnBi$_2$Te$_4$ (MBT) materials are promising antiferromagnetic topological insulators where field driven ferromagnetism is predicted to cause a transition between axion insulator and Weyl semimetallic states. However, the presence of coupling Mn/Bi antisite defects main Mn layer can reduce low-field magnetization, it has been shown that such more prevalent in structurally identical trivial magnetic MnSb$_2$Te$_4$ (MST). We use high-field magnetization measurements show MBT MST occur stages full saturation requires fields of~$\sim$~60 Tesla. As consequence, plateau state MBT, many determinations quantum anomalous Hall studied, actually consists ferrimagnetic septuple blocks containing both uniform staggered component.