Dear Savithri ji,
It is a fine categorization of curriculum stages, but with respect to the stage names, I think the ‘middle’ seems to be not a perfect name for a curriculum stage. Similarly if the name Senior Secondary had come after Secondary it would have been more self-explanatory than the existing pattern. If it makes some sense please trigger a discussion at NCERT.
US and UK also refers to 6-8 as middle. As also many other places. Ur reaction! Savithri