After his wife's death from misdiagnosed cancer

[Bassim]

I am wondering if my sentences are grammatically correct.

After his wife's death from misdiagnosed cancer, Peter could hardly contain his fury at the doctors and the hospital. He couldn't believe that such disastrous mistakes could be possible in the 21st century.

 

[Phaedrus]

He couldn't believe that such disastrous mistakes could be possible in the 21st century.

I think that sentence would be improved upon if "could be" were replaced by "were":

He couldn't believe that such disastrous mistakes were possible in the 21st century.

 

[emsr2d2]

The phrase "misdiagnosed cancer" is potentially a little ambiguous. When I read it, I wasn't sure if she had cancer but it had been misdiagnosed as something else, if she had cancer but it was missed completely and she was diagnosed with nothing, or if she died of something else but had been given an incorrect diagnosis of cancer.

 

[Tdol]

Misdiagnosed or undiagnosed?