Also, one has to keep in mind that there has been innovation in table tennis over the years, people finding "new" strokes and ways to play. Something that is thought to be the "proper" way to do something doesn't have to be the best way to do it, even if it might be the best known way.
Not correcting things that are seen as technical flaws might become the new proper way to do it in the future. An example of this is the Swedish ski jumper Jan Boklöv. His technique was seen as improper and he used to be gutted by the judges. Today almost all ski jumpers use his technique.
I like this post a lot!!
I am a case in point, I was taught to play initially by coaches in Sweden as a kid in the 1970s. In terms of mechanics, coaches in the last several years have actually worked with me to
un-learn some things I was specifically taught as a junior, but which are now obsolete. I have been able to make
some of the changes. But not all. It is definitely hard for me to get the wrist motion that gives the most massive spin. My footwork is instinctively inefficient (not helped by age).
What we needed to do in the 1970s to loop a ball with slow blades, slower rubbers, and no speed glue was a bit different from what is required with an ALC blade with Tenergy 05, or speed-glued Bryce for that matter. Also people had just not thought that deeply about how to hit things more efficiently. Heavy 40 and 40+ balls sink faster, and they allow a lot better counterlooping right off the bounce, and there are things you can do with them offensively that you couldn't ever do with a 38mm ball because they would fly off the table. That means you need new footwork habits and even a different mindset now. Some of this is easier to learn than others. And if you look back at serving in the late 70s and early 80s, it is utterly primitive compared to what happens now. Things evolve.
It is very hard to change
some of the things I do. I have tried and know it's just not going to happen. The best coaches have recognized that some of those things are "good enough". Other things I have picked up on easily.
One of the best players of my junior era was Dragutin Surbek, a strong monster of a looper (one of my heroes but in those days almost impossible to find videos).
You wouldn't teach someone to loop like that now!! By contrast, his contemporary the late Kjell (Hammer) Johannson looks a lot more modern. Klampar, one of the first to hit really strong backhand loops, looks pretty stiff now. Stellan Berngtsson had the most modern looking footwork of that era IMHO (also one of the first guys to mostly serve short). Moving forward, if you can find videos of Waldner at 16, it still looks like an earlier era, but he looks more modern later, and he was a huge serving innovator. Gatien was one of the first to really counter right off the bounce with such power.
Players with older techniques can still be pretty good at an amateur level. But they are not going to make it into the top echelons. Kids, you teach them to do it the modern way. Adults? Yes, if they can. But sometimes they can't.