I agree also that there are some unclear things in this business.
For example, I purchased " how to teach your baby to swim". While reading it I found that it is only about the newborn babies. Swimming is started in the first weeks, and than continued and developed. Chapters like "how to teach 2 years old" is about babies which started to swim as newborns.
My child was 18 monts old, and there was no single sentence that swimming can be started in this age. When I tried to start swimming with my doughter, she just cried and did not allow me anything. In this age, children often don't allow to wash their hair. Of course, such children don't want to be immersed in water. May be there can be some recommendations for such children but they are not in this book.
Something like "dont't buy this book if your child is older than 6 months" should be mentioned in introduction or in amazon description but it is not.
Of course, there is a word " baby" in the name of a book. But I thought that this method, similarly as with reading, can be started at any age. Probably many parents spend their money on book which they can not use.
Concerning updates in the newest GD books.
I purchased my books 5 months ago from amazon.co.uk.
" How to multiply..." is copyrighted from 2005.
May be there are some updates but they might be very minor and unsignificant.
In chapter about the reading, there is about the use of that strange paper size. Like every other paper size is poisonous. But now, everyone is using A4. Why not?
There is even a comment on use of stencils (who will use them in the age of computers?) but there is not anything about the use of computers. Well, here is said that you can use computer for printing. But computer is something more than just a printer.
So, this book still is (and will be) half century old.
In general, I think that GD method is great. But it was published in sixties and have not much changed from that. And it is OK. Other authors continue his work.
It is as like as with photography. In sixties, there were black and white photos which were developed manually. Nowdays, if we want to make good pictures, we use basic recomendations from old times but we don't need to follow all the recomendations on how to manually develop pictures in bathroom, in red light