Each thread of a multithreaded program can obtain its own copy of the PISDK object. PIPoint's are cached below each SDK object. So if different threads of the same program are editing PIPoint's, they will overwrite the changes of the other. The last writer wins.
The same is true for more than one program running at the same time. Each program gets its own copy of the PISDK object and its cache. If each program edits PIPoint's, the last one which writes will overwrite the changes of the other.