"Guadalupe will be its destination in the week preceding any voyage it makes to Jamaica."
This is a really good rule to learn from, because I have seen multiple people similarly misunderstand it.
It is true that J must always have G come before it.
J - - - > GJ
However, if there is no voyage to Jamaica in week 4, then that rule is no longer relevant. The sufficient condition is not present, so we do not have to worry about the necessary.
In other words, G is not tied to J. G can exist without J, but not the other way around. I'll create an example.
M T G M G J T
Does this satisfy the 4th rule? Yes, because any voyage made to Jamaica is preceded by a voyage to Guadalupe!
