So they give 30 days to submit new photos but they get to your new photos only after around a month. Also you cannot verify if they received your new photos until they get to processing your new photos. And if they do not receive your new photos within 30 days you have to apply for the PR card again.
Getting back to a previous application on receipt of additional documents depends on the officer who is handling your case. After the documents are received, they are checked and double checked by superiors for approval. Then only, they are accepted.
If in doubt about whether IRCC has received your additional documents, we can always send them a case specific enquiry through online form. But first, we need to make sure that our package was delivered to them. In my case, I've always used Canada Post for sending documents or passports to IRCC offices.
IRCC CPC offices are large volume receivers and they don't collect every package sent to them personally. All our packages go to their mailbox. IRCC representative collects mails every other day. These mails are sorted and passed on to respective case officer. I always cross check with Canada post customer support regarding delivery confirmation, if I don't get confirmation from their tracking page.
If we don't see an update on our application within a week of delivery, we should always send them a case specific enquiry. Sometimes, the application is not updated even after additional documents are successfully delivered till the case officer has checked all docs.
Hope, this information is of help to everyone.
Have a good one.
Jai Mahismati