Demonstration Discs - particularly white label ones from USA - tend to match retail builds of the titles. However, it's not uncommon to discover a pre-release beta build among them. For me, this has made the particularly interesting to hunt down and dump (although it's a process I wish I started on earlier as they have become scarcer these past few years).
Demonstration Discs are not "demo" discs, rather they're full game promos. Commonly promos are given to press to review games - often before release. If a bug is identified before the retail pressing begins, an update will be issued when the game comes out in retail. However, sometimes an update is issued while still in promo phase. So far with CDi, this has been a rare occurrence (at least as far as the data I've collected shows). Dragon's Lair II and Classical Jukebox are the only two examples I've found where a game promo was pressed twice (each time with a different code revision).