@Kool ******
It doesn't matter how many times it hasn't been checked. What counts is that as soon as there is an instance when it DID happen, from then on you have to take into account that an official at Jaeng Watthana immigration MAY require your bankbook for the transfer of stamps.
I know of a 100% true case a few months ago where he had to come back the next day with the bankbook (but luckily could cut the queue).
This also means that anyone who used an agent to circumvent the money requirements suddenly gets into unforeseen problems.