I remember that my first CD player in 1985 or so, which was a Pioneer had an Index feature. Certain CDs in the early days of CD used to have additional track markers within each track called indexes. You could hit the Index button and advance to those tracks-within-a-track. Too bad that feature never caught on.
Yes, Index points were a sensible way of allowing for intra-track access. Telarc and Denon both seemed quite committed to them for a while, then they were gradually phased out as fewer and fewer players were able to deal with them. I had a Philips-based Mission player and a couple of Sonys that would do Indexes, and then no more.
I dislike Track numbers used this way because, when I want to hear the second movement of something and push [2], I'll get some random spot in the first movement. Then I have to either push >> an indeterminate number of times, or go consult the CD booklet to discover that I should really have pushed [7]. Admittedly, a minor issue.
James