So it seems to be an open issue now. So I guess until this is done I will have to rely on .NET Core API reference and pray I won\'t hit one of the 43 API
netstandard2.0 is mostly determined as netstandard1.6 plus those methods in mscorlib.dll, System.dll, or System.Core.dll in both the .Net Framework 4.6.1 and the current version of Xamarin. There are still small changes happening, which can be seen via the commit and PR history at https://github.com/dotnet/standard/
The methods that existed in netstandard1.6 but aren't in .NET 4.6.1 were marked as not visible to intellisense to prevent confusion from new developers. But they do exist, so you can successfully compile if you write the code anyways. That was the compromise attained for "but it won't work on netfx" and "but I can't upgrade my netstandard1.6 library".