It's why the original Matrix DVD dual layer release was so hard to duplicate / replicate by pirates/"enthusiasts" in a way that would fit on single layer DVDs. One of those was a secret "follow the white rabbit" mode that lead to hidden content.
Unlikely. All players manufactured had to pass DVD specification testing. This is not to say that there were not hardware bugs in early manufacturing runs, but the realities of shipping hardware players prior to widespread, cheap and consumer-friendly firmware update methods meant there were far fewer bugs and hardly any showstoppers. The limiting factor for amazing presentation features was and is authoring platform support, and it's astonishing how many older authoring platforms supported these features even though their newer updated versions dropped support for them (e.g. karaoke-style subtitles in Maestro lost in DVD Studio Pro... and don't get me started on support for seamless story branching). Player devices and commercial software had to support all the features to sport an official DVD logo, and ones that didn't (or did and failed to pay the patent licensor) were sued out of existence.
Yeah, early on in the DVD era having deleted scenes and commentary tracks was totally new and a big deal for a lot of us.
In the peak of the DVD era my SO and I were both big movie fans, and at one point had watched literally everything the Blockbuster and Hollywood video in our neighborhood had. There just wasn't the embarrassment of riches of the post youtube world.
That blew my mind and was an awesome experience. In the age of dial-up internet it wasn't like you could find and / or watch that online.