This below for example is from MSV Trackdays
I'm not seeing anything on No Limits website... but you never know.Wearing a back protector makes sense. Up until now we have always 'strongly recommended' riders to wear one. From 2022 this has been upgraded to being compulsory. When lining up for your sighting laps the pitlane marshals will do their visual checks (for wristbands etc) and give you a friendly pat on the back which may be accompanied with a prod or two to see if you are ticklish. The back protector should be full length to cover at least the majority of your spine. The back protector can be integrated or separate. The back protector needs to be designed and fit for that purpose.
I had a go with my leathers today and they're shall we say, "a bit snug" once i shoehorn in a back-protector. So you may want to check yours just to ensure you can get into them