The two rules are Methods 1 and 3 in https://sciencing.com/how-to-name-covalent-compounds-13712167.html
Given that the electronegativities of C, Si, N, P, S, O are approx. 2.5, 1.8, 3.0, 2.1, 2.5, , 3.5, resp., one of these rules has to give.
Thanks.