When I was Silver with LH (working in MUC for 18 mths), I used the Silver for the next year after leaving.
BUT in the week when it fell due . the LH computer duly sent me a new grey card with a different number, so that I could not use the old one any more! Such efficiency and concern that you only get what you paid (through the nose) for.
I still have the Silver Luggage Tags and use them when on a Star Alliance carrier but doubt that they do any good!