Realistically is this a ticket… or am I over thinking

I was driving on the M40 near High Wycombe towards Reading when I passed a small, portable electronic 40 mph sign that was easy to miss. There were some closed roads and no further signs it was literally a small digital board on the side of the road. I didn’t notice any average-speed cameras, fixed cameras, or camera vans, and Waze didn’t warn me about anything. I carried on driving at around 50–70 mph for a few miles, and other traffic around me was also going faster than 40. It was only when I saw an ‘end’ sign further along that I realised the 40 limit had been in effect for longer than I’d thought. It was not an average speed zone with continuous speed cameras over a gantry or pole.