Looks like you're right, I just saw it in the Windows SDK winnt.h file, it's defined as:

#define CREATE_BOUNDARY_DESCRIPTOR_ADD_APPCONTAINER_SID 0x1

I'm not sure on which line to add it to, is it okay to add it on line 3750, before #define SID_REVISION?

How come they used the value 0x1? It's 0x01 on the Microsoft Docs site. As far as I know, they are the same value but differ in bit value and the compiler evaluates them to the same value. So for copyright purposes, would it be better to add or remove extra 0s? Should I do the same for PRIVATE_NAMESPACE_FLAG_DESTROY?