From what I remember of the Red Book, it's not so much what it does specify, but what it doesn't, unfortunately. A lot of the things can be done to the disks without them apparently contravening the standard - the trick is in implmenting the fudges without it directly affecting playback (or maybe in some cases, with it affecting playback, quite deliberately! ). We used to embed test tracks and all sorts on many pressings, including (most famously) the one that lauched CD as a standard, "Brothers in Arms". If you know where to look on an original early pressing of this CD, you might get a few surprises - I wonder why there are only a few tracks on that CD?

A lot of the later stuff (high density, and so forth) that got put out as enhanced disks usually were taking advantage of slopiness in the spec - for example, there is no physical boundary on an audio track, as long as it terminates with a logical symbol as an end of track marker. So if your player is capabable of tracking far enough out, what's to stop a track going over what used to be the physical boundary normally imposed by the reliability of the production processing at the edge of the disk? If your sputtering deposition process is uniform right out to the edge of the disk with no degradation, then you have more room for a track to extend out the disk to 80 odd minutes and there is nothing to stop a well-designed CD head from going out that far.

The reason the original CD-A disks got pegged at 74 minutes was because the early disk production equipment couldn't reliably deposit the reflective material beyond about 3 mm from the outer edges of the disk. This meant that as you got into the "Dead Band" at the edge of the disk, the symbol error rate from the decoder reading the data stream skyrocketed. So Philips and Sony simply designed their production stampers (that got sold to the people producing CDs) to always stamp inside the reliable deposition radius of the disks, giving a practical recording time limit of 74 minutes! This ensured that their QA were happy with the playback quality all across the disk surface and that the number of disks with "Defective last tracks" was minimal. Public perception of the product never suffered as a result, and the rest is history.

I must dig out my old (and very dog-eared) copy sometime....