I think you should talk to your drugs squad. Is it not a coincidence or significant that you are the sole beneficiary, or would have been a sole beneficiary, of a forged will. There is nobody else who could have sent that letter who had an interest in the estate of Mrs Grundy other than yourself, after her death. Not with the doctor's typewriter they couldn't. And who would have been aware that the will had been deposited with Hamilton Wards when the original will had been with the daughter.
People do die suddenly of old age.
They just wear out. So no, I don't think it was peculiar not to ask for a post mortem. You don't keep drugs in your surgery. I keep no drugs, you are talking about controlled drugs, in my surgery, my car or at home. We'll have a short break.