In time, Raymond Franz was assigned as branch servant to the Dominican Republic, he served there during the time of tanks in the streets and bullets pinging off buildings in the capital city. After Bro. R. Franz left the Dominican Republic to go to NY a brother and sister, Gilead couple, Vincent and Judy Irizarry were assigned there and continued the Branch work in the midst of a lot of turmoil. This couple who now lives in North Central Massachussetts isn't even mentioned in the yearbooks, yet it was people like them who continued steadfast in their assignments when the military situation got nasty. They can tell about how it really was in the Dominican Republic of those days.
But the 2015 mentions WT President Knorr and Freddy Franz visiting and giving talks (when it was safe), as if this was the reason for the increase. The WT HQ wasn't responsible for any increase, it was those who put their necks out during the time of military turmoil, and went through the hardship of those uncertain days that were brave enough to stay where they were assigned to preach.