In reply to Chris Craggs:
Looking at the online instructions and form, I think the system is the same one that has been in place for at least the last 2 years, certainly the last 2 winters when we've been there. It's NOT a permit to rock climb on the Penon, and no permit is needed for that. It is simply a permit to access the "Ruta Roja", which is the tourist path to the summit (and I guess it is named due to the red paint markers on the route).
It was brought in to try to manage numbers, and is mainly enforced/checked/whatever during busy times, and certainly, the last 3 times we've gone up the Penon (in December/January), the office at the visitor centre has been closed and no sign of any officials. BUT we do know 2 friends that were stopped in January last year at the office, told they needed a permit, and were guided through getting one on the spot.
It would apply to any climber coming down the path after doing a climb, so there are 2 obvious solutions to avoid the possibility of being stopped or fined - come down so late all the officials/rangers have gone home (we regularly see headtorches coming down, from our apartment balcony!), or, maybe preferable, just get a permit - yes, it's a bit clunky, but perfectly doable, and it's free. The only problem with that is that the online system doesn't let you do that on the day - it only shows dates from the next day onwards. It's a simple PDF form that can be shown on a phone, or printed off.
Cheers, Andy