Your api viewer file is out of date.

Go to MSDN and download the Platform SDK files. These have the latest C++ header files for Windows in which all these constants are defined.

For your info:
EM_STREAMIN is defined in Richedit.h as:
#define EM_STREAMIN (WM_USER + 73)

since Public Const WM_USER = &H400
then Pucblic Const EM_STREAMIN = &H425

HTH,
Duncan