I tried reading a 7.0 file (containing a structure with a matrix field) and that file could be read with the same low-level code as 7.3., i.e. the patch below seemed to work correctly: ...

Pure Go library for reading and writing MATLAB .mat files (v5-v7.3+). No CGo, no external dependencies. Full support for numeric types, complex numbers, and multi-dimensional arrays. Cross-platform ...