@Imperious-Leader
I see no mention on page 23 of sea zone numbers. Only this:
“You can place sea units only in sea zones adjacent to territories containing eligible industrial complexes. New sea units can enter play even in a hostile sea zone. No combat occurs because the Conduct Combat phase is over.”
If you look at page 8, you WILL see this:
“Note: The Caspian Sea (surrounded by Caucasus, Kazakhstan, Turkmenistan, Eastern Persia, Persia, and Northwest Persia) is considered to be a sea zone, even though it does not have a number.”
I suggest you recheck the rules. You might be looking at the wrong book.