The problem about netstandard.dll

The System.Collections.Generic.Dictionary in runtime is located in “/Applications/Unity/Hub/Editor/2019.1.2f1/Unity.app/Contents/NetStandard/ref/2.0.0/netstandard.dll” and the count of constructors is 6, but when I used reflection to get it, it’s location is “/Applications/Unity/Hub/Editor/2019.1.2f1/Unity.app/Contents/MonoBleedingEdge/lib/mono/unityjit/Facades/netstandard.dll” and the count of constructors is 8,

the runtime and the reflection don’t match , why?

The API exposed by netstandard.dll is a proper subset of the API that is actually run against. The implementation that code is run against likely has a larger API surface than is exposed in the reference assemblies.

Thanks for your lightening reply.
I wanna use reflection to generate some code for lua, so what should I know the differences exactly?