As I understand it I can't dump physical games without the MS dumper or a modded switch so when you say "elsewhere" I think I know what that means.
I've seen dumps where the game has only "XCI" but others where it has "XCI", "NSP" and "NSZ". What do these actually mean? Can I make do with just "XCI"?
EDIT: bit of googling... so NSP is Eshop software and NSZ is some sort of converted file. So I'm guessing I only need the XCI files?
the migswitch is a cartridge emulator. an xci is not a complete cartridge, just the data partition basically. you need a bunch of additional files beyond the xci to emulate a full cartridge. those files are created when you use the mig dumper, and they can be created by nxdumptool when you are dumping yourself from a modded switch. but they're not available on any pirate sites since each cartridge contains a unique certificate and noone wants to ruin their own cartridge.
congratulations, you've bought a paper weight