Since my renaissance seriously starting practising the piano again I have followed Thomas Matthay`s book titled: "The Visible and Invisible in Piano Technique" which I bought years ago in a second hand book shop. It has now occurred to me that since he wrote that book some changes and improvements might have taken place in piano technique and I wonder if any members can advise me if I should drop it for something more appropriate and useful for modern times.
Thank you

No, there's been no change but you need a teacher. I have all his books but understood nothing until I found an ex-student of his years ago.