PIP - reporting improvement in condition?

My son who is 19 receives PIP (higher rate living, lower rate mobility), his conditions are speech and language impairment, autism and dyspraxia. He is 19, claimed PIP at 16 after DLA and I am his appointee. His award is until Oct 2024. For mobility, at the time, he was awarded it because couldn't ask for directions when out walking, couldn't use public transport without assistance, but no physical impairment. In the last year his confidence has grown and he is now using public transport with only prompting rather than assistance and is becoming more adventurous and going further afield. On the other hand he is still not at the level of a typical 19 year old who might be going on holiday abroad without adult help and is finding learning to drive very difficult compared to an average teenager, so there is still need. He has just completed his first year at university with a LOT of support from family, DSA and the uni services so I consider his living needs unchanged, it is just the mobility.

So my question is should I report this change, is it likely to mean a complete reassessment, or is it safe to leave it till his review next year on the basis that between ages 16 and 20 a lot can change for people with his conditions and would be expected? If we leave it to the review are they going to ask when the changes occurred and make him pay it back? Hard because they are gradual. We really, really do not want to get into trouble for overclaiming but on the other hand a complete reassessment is a daunting prospect. If we were found to have overclaimed would it just be a repayment plan or fines etc.

Thank you, I appreciate your response. From the self test he should still be eligible for higher living but not for mobility. If I report this change will they want to do a complete reassessment for both elements?

Thanks, yes, I did keep all the responses I submitted for the initial claim. I'll ring them up and start the ball rolling.