(1)
In the documentation for loads(), the name for the first argument of loads is 'bytes_object'. The actual signature, both in pickle.py and _pickle.c, it is instead 'data'.

(2)
In the documentation and in pickle.py, the default value for the 'buffers' parameter is None. However, in _pickle.c, it is an empty tuple (); this is also reflected by running the interpreter:

In [1]: inspect.signature(pickle.loads).parameters['buffers']                                                                                                                                                                                                    
Out[1]: <Parameter "buffers=()">

Thanks to @hauntsaninja for spotting these in https://github.com/python/typeshed/pull/3636