Speed limit on the #SouthCircular (A London main road) was reduced to 20mph in March last year (I tooted about it back then : https://rouge.eu.org/@jfparis/112095838578504118). I updated #OpenStreetMap straight immediately at the time.
Today I used a #ZipCar (car pooling). It was a car with 25 plates (means sold after 1st March 2025) and the onboard navigation was still showing me 30mph.
Underwhelmed to say the least