Does ritual impurity transfer to the outer garment if no trace of wetness from the impurity appears on the inner garments after sitting for a long time?

A pure item is not ruled to be impure except with certainty, and doubt about the transfer of impurity is not considered. So, unless you are certain that impurity has transferred from the inner clothes to the outer ones, while both or one of them is wet, the outer clothes do not become impure. You must cast away doubts and ignore them.