There was an earlier topic on this very subject:
IIRC the date at 4b concerns the requirement for a medical for certain types of vehicle/trailer combination. If eg you are towing a “heavy” trailer (unless the law has changed) up to the age of 60 in class E/B a medical will be required every 5 years (up to the age of 60) every 2 years over the age of 60 and annually over 70. If you do not drive that class of vehicle (even though your licence covers you for it) you will not need to action the medical requirement.
The old style permis (3 fold) only expires when you do 