I have a similair question to the question here, but regarding a different book.
"Principles of Quantum Mechanics" is a 1930 work by British Nobel laureate Paul Dirac. The wikipedia article on this book states that there have been a couple of editions (with improvements and additions), the latest being the 4th edition, published in 1958 (6 years before the Feynman lectures were published). This is a long time ago and I'm wondering if parts of the book are outdated, and if so, which ones and why?