これだろ
>V1 GUIDs which contain a MAC address and time can be identified by the digit "1"
> in the first position of the third group of digits, for example {2F1E4FC0-81FD-11DA-9156-00036A0F876A}.
>V4 GUIDs use the later algorithm, which is a pseudo-random number.
VSやC#コンパイラのはどっちかは知らんが