The notice was deemed to be delivered on 11 May.
This is more than 14 days after the alleged transgression.
If the driver is not identified, the registered keeper should appeal on the basis that PoFA 2012 can not be used to transfer the liability from the unknown driver to the registered keeper because the notice was issued too late.
Search the forum to find an appropriate appeal, and feel free to post it here before sending to be sure.
See
https://www.legislation.gov.uk/ukpga/2012/9/schedule/4Unlike many of their brethren, NCP has history of actually cancelling following valid appeals like this.