You don't use sites with numbers in Open, Standard or similar formats. The rules about choosing a site, adding twilight for region etc. apply only to numberless sites.
For official formats, you always use the most recent site path in a given format. For example, if you're playing with Fellowship and Towers cards, you use Towers sites. If you're playing sets 1-7 (7 being the first ROTK set), you use King sites. As soon as you involve set 11 (Shadows) you use numberless sites.
You never mix numberless sites with sites that have numbers, since the rules regarding them are fundamentally different.