2:17　SmCo　magnets　with　a　quinary　composition　of　Sm(Co,Cu,Fe,Zr)7+δ　are　industrially-relevant　hard　magnets　used　in　high　temperature　and　corrosive　environments.　Their　complex　cellular/lamellar　nanostructure,　consisting　of　ordered　2:17　phase　cells,　1:5　phase　cell　boundaries　and　Z-phase　(Zr-rich)　lamellae,　is　essential　for　their　high　coercivity.　However,　the　system＇s　complexity　makes　it　challenging　to　determine　the　contribution　of　each　element　or　microstructural　feature　to　coercivity.　To　disentangle　the　microstructure-property　relationships,　we　simplified　the　system　to　binary　and　ternary　SmCo7.7-xZrx　(with　x=0and0.1)　magnets　and　conducted　detailed　micro-　to　atomic-scale　analyses.　Only　Zr-containing　magnets　formed　a　cellular/lamellar　nanostructure　akin　to　industrial　magnets,　in　Zr-rich　regions　with　at　least　1.4　at.%　Zr,　but　without　achieving　high　coercivity　due　to　low　elemental　gradients　in　absence　of　Cu　across　cell　boundaries.　Data　from　Zr-poor　areas　of　SmCo7.6Zr0.1　suggests　that　2:17　phase　twin　boundaries　facilitate　cellular　nanostructure　formation　by　providing　inhomogeneities　for　heterogeneous　nucleation.　©　2024　The　Author(s)