The most limiting factor is simple ... the MIND. I know its hard to get ones head around it but the mind limits us (as humans) in so many ways. I have created a positive sigil for penis enlargement and using that along with exercise works for me. Length will be limiting if you allow thoughts to sneak in and anchor. Sure some things become harder, like gaining length with a thick penis such as myself but with perseverance and dedication it comes.
The cord you mention is something I have heard about time and time again. I would need to do research on it to give me feedback on that but it shouldn't limit you in length gains, even if its stubborn with enough force and intensity overtime it has no option but to adapt and by that it will grow.