Hi
Considering only 2nd bullet point. SG implements it on SW2, SW3 and SW4's trunk links for not allowing vlan 102. The same solution can also be implemented via either of the below two ways
1. only SW3
int range f0/16 - 20
switchport trunk allowed vlan 1-101,103-4094
OR
2. Only on SW2 and SW4
on SW2
int range f0/16 - 18
switchport trunk allowed vlan 1-101,103-4094
on SW4
int range f0/19 - 20
switchport trunk allowed vlan 1-101,103-4094
Why SG implements this solution by configuring SW2, SW3 and SW4.?