The scene is rife with fake or malicious NSP files. Use these checks:
No. An update NSP is a patch – it requires the base game already installed (either as NSP or XCI) on the same system or emulator NAND. Donkey-Kong-Country-Tropical-Freeze-NSP-Update-...
Yes. Offline installation via TinWoo or DBI does not require Nintendo servers. Just ensure you have valid SigPatches. The scene is rife with fake or malicious NSP files