PIP awarded for ongoing period ??

Hello my son has got his descision on pip, enhanced for both care and mobility. I would first of all like to thank you all at B & W for your priceless guides and seemingly endless questions I've asked over the last few months but your advice has been carried out to the letter.
Anyone going through the process of ESA or PIP system needs to consult the members guides and follow their advice as without it success is very much stacked against them.
My question is that there does not seem to be a period of time given other than an ongoing period ? Have any other me people been given this same award and what exactly does it mean ? can they actually come back to him at any period to have a further assessment, rather confusing and would appreciate any light being shed on these types of awards/period and what is meant by it. Special thanks to Gordon and of course B & W

Thank you Gordpn for your reply. That is very interesting I'll keep you updated on any future reassessment request.
thanks again for all your advice