When is a change in an ability actually a significant change?

Hello! I've been worrying about whether it's necessary to report a change in my son's ability to follow a familiar journey. He is 16, autistic and the PIP claim was only made last year. He was awarded the enhanced rate for mobility. At the time, he wouldn't even go out the front door on his own, let alone follow a journey. Since then, I spent a long time building his confidence and teaching him the route to college. He is now able to follow it on his own, and catches the train (as long as I have purchased the ticket for him in advance), but if there are any changes (as there have been in last couple of weeks) or he makes a mistake and e.g., ends up on the wrong train/going the wrong way (both of which have happened), he gets very distressed and contacts me. I have to calm him down and talk him through what to do or else pick him up. He is still unable to plan a route on his own. He doesn't go out on his own for any other reason.

I am autistic too and also in receipt of PIP and the whole application process is a huge source of stress for me (last year it engulfed all my time, energy and focus so that I couldn't handle other activities and felt like I was in a constant state of overwhelm) and I also had to renew my own PIP shortly afterwards! Therefore, the last thing I want to do is stir everything up again with the DWP (I have enough stuff going on mentally/emotionally), and risk his whole claim being re-assessed. Can I just leave it for now, unless he manages to start doing other journeys on his own and becomes more confident with changes/asking people for help etc.?

Thanks for taking the time to read. I would be grateful for some advice.