Fact. Nothing is checked in terms of verification of the signature.
I have signed over 50 life certs in the last 10 years. Initially I added a stamp and phone number - never any follow up contact.
Now, virtually anyone can certify the life certificates.
I imagine that somewhere in Wolverhampton a junior clerk ticks a box on your record to evidence return. Only by default, ie non-return, does the system flag up the fact - and payments are suspended.