In my experience, port fee increases after PIF aren't passed onto passengers. The only time we've ever had it happen was on our first
DCL cruise (Panama Canal). After the PIF date the charge (per passenger) increased something like $100. DCL applied it to everyone's bill and got such an uproar, they dropped it and ate the upcharge.
IMO, that's typically how it happens, after PIF no additional charges. The cruise lines tend to charge the port fees and such over current pricing, hoping to cover any raises.