Hi Mayank
I don't know if there are special requirements for ND but generally speaking it is recommended to submit your PCC with the application for two reasons:
1. If you haven't submitted it then once ND receives your application an additional document request will be sent and then they wait for you to submit etc. If they already have everything and there are no other concerns with your application, they may just issue a visa. To avoid delays, it is best to submit your PCC with the application.
2. PCCs are valid for only 3 months. If you obtain your PCC and submit it right away with your application, this is straight forward. If you wish to submit it later, you need to time everything correctly so that the PCC is still valid when you submit it. This can be difficult as you don't know exactly how long it will take to get the PCC or when ND will get around to requesting it. If you time it incorrectly, you risk your PCC expiring or not having it ready in time to submit within the deadline they will give you (usually 90 days).
So - no, you do not have to submit your PCC with the application BUT it does make things easier. Again - I don't know why the checklist specificies that after June 26 it is strongly encouraged but I would guess it is because they are processing quickly and waiting for a PCC would cause considerable delay for you.