I had reason to query the NRNB rule regarding ante post bets at RA with b365 on the Monday before the meeting started.
This was their response :-
"......Thank you for your message in regards to placing selections on Racing, non runner no bet.
Please be advised that races will change to non runner no bet approximately 48 hours before the race is due to start. With this in mind, racing on the Tuesday and Wednesday at Royal Ascot is now non runner no bet.
At the point of a race becoming Non-Runner No Bet it will also qualify for the Best Odds Guaranteed offer......."