Caution: imperfect analogy following.
Imagine lifting a stone with a rubber band. At first the rubber band will stretch as you pull on it, while the stone won’t move. After stretching the band to a certain amount the stone will be lifted up from the ground.
It’s a bit like that. Your FSL will increase for a while, and eventually erect length will start increasing as well. In my case FSL increased for two months while erect length stayed put. Then, two months ago, my erect length started increasing as well and has stuck to about the same rate as my FSL gains since.
April 2017: 6.5" BPEL -> July 2017: 7" BPEL
New goal for 2019: 5+ inches girth
My length routine: a few single 1-minute fulcrum stretches a day. Yes, that's all.