Most important be patient and watch it. When ive been close to harvest in the flushing stage or close to it, but wanting more trichs ive used a brand from bio-bizz or buzz called top max or an aerobic tea of just worm casts then adding molasses before feed. Theres other products you can use later in flower too. Fyi Molasses is an acidifier, will lower pH sometimes acidic nutes pushes more development. Me, I wait and tea or massive flush then see response. But waiting to long can herm out or mold outdoors.
You are correct dont count the stretch for flowering weeks. Each strain finishes differently. Some take a while to start getting big. Some dont develop nose and trichs till way later in flowering. Some need more than the quoted weeks flowering. All of us are not growing in the same way as the breeder or seed company that made the strain so expect longer.