Thats funny to hear, I had a minidisc player as a young tech neophyte in North America and never had compatibility issues, or even until now knew there were variants of md.
The variants came along a good few years after MD hardware went on sale in the US - the first MiniDisc player went on sale in the US in September 1992, while NetMD wasn't introduced until 2001 and Hi-MD in 2004.
With the original iPod also introduced in 2001, and MD's high media cost and lack of pre-recorded releases having kept it firmly in its original niche, I think probably most MD adopters in the US didn't have compatibility problems for the simple reason that, by the time those problems became possible, we weren't really bothering with MiniDisc any more anyway.
That said, NetMD was just a different format on the same media, and a line of players capable of transferring audio from a computer digitally via USB. You can't use a NetMD-formatted disc in a non-NetMD player, but you can still reformat and use the disc in an older player, and a NetMD player will play back discs using the older format. The real compatibility barrier is Hi-MD, which uses a totally different media formulation in order to reach its ~1GB capacity; as far as I know, Hi-MD media, however formatted, can't be used in any non Hi-MD player.
(Even for latter-day MiniDisc aficionados such as myself, that's still not a huge barrier, because not much Hi-MD media was ever made, and you can expect to pay $60 or more for a single disc today. Hi-MD players are likewise rare and pricey, so I suspect most folks who get into the medium for hobby reasons end up sticking with NetMD.)
I don't think MD-Data ever made it to consumer availability in the US, but you're not entirely wrong with regard to fragmentation. That said, Sony seemed to do a pretty good job of keeping it under control in the US prior to the release of NetMD in 2001, but I suspect "seemed" is the operative word there, and that it had less to do with effective management of the medium on Sony's part and more with the whole thing being an incredibly tiny niche in the US for its entire lifespan.
Sony certainly doesn't have a good enough record on avoiding media fragmentation generally, that any benefit of the doubt seems warranted here...
With the original iPod also introduced in 2001, and MD's high media cost and lack of pre-recorded releases having kept it firmly in its original niche, I think probably most MD adopters in the US didn't have compatibility problems for the simple reason that, by the time those problems became possible, we weren't really bothering with MiniDisc any more anyway.
That said, NetMD was just a different format on the same media, and a line of players capable of transferring audio from a computer digitally via USB. You can't use a NetMD-formatted disc in a non-NetMD player, but you can still reformat and use the disc in an older player, and a NetMD player will play back discs using the older format. The real compatibility barrier is Hi-MD, which uses a totally different media formulation in order to reach its ~1GB capacity; as far as I know, Hi-MD media, however formatted, can't be used in any non Hi-MD player.
(Even for latter-day MiniDisc aficionados such as myself, that's still not a huge barrier, because not much Hi-MD media was ever made, and you can expect to pay $60 or more for a single disc today. Hi-MD players are likewise rare and pricey, so I suspect most folks who get into the medium for hobby reasons end up sticking with NetMD.)