Many writers have attempted to divide Next Generation Sequencing into Second Generation Sequencing and Third Generation Sequencing. Personally, I think it isn't helpful and just confuses matters. I'm not the biggest fan of Next Generation Sequencing (NGS) to start with, as like "post-modern architecture" (or heck, "modern architecture") it isn't future-proofed.
Keith Robison gives an interesting deep dive on how sequencing technologies have been named and potentially could be named.
This post reminded me of my previous takes on the confusing, and inconsistent labelling of these technologies: