The treatment of the systems of equations as discussed in the course book is an interpretation of the Code. The errata was correcting the interpretation, not changing the Code. Systems of equations are spatial and would be preceded and followed by blank lines, regardless of the presence (or not) of enlarged grouping symbols. That definition got muddied because the only discussion about systems of equations in the Code was in the section about enlarged grouping symbols.
I don't know if that clarifies the situation. The Nemeth test is a test of the code and not a test of the course. The course book should only be used to help understand what is written in the code, not to base your decisions on.