Large sections have completely been rewritten I noticed several months back when I went looking too. And I guess it is still a work in progress. Huge site really. Will take a while to update. Much of what’s been made to look different, modernised? seems to just have been copied block by block into the updated format but no doubt he’s updating where he feels necessary as he goes.
The site engine is a more dramatic change, but content has surely always been evolving on an ongoing basis? He puts a date of last update on most pages at the top. eg MAV page was apparently updated last in June 2018 Vestibular Migraine
Duplicating content here is not a good plan and in this case we should defer to Dr. Hain and his discretion over what is maintained on his site. As far as off-site content is concerned, in general, there should really be only one copy of everything and we should link to it. By linking we leverage the work of the remote site to manage their content so there is less risk it will age and we won’t be hit with copyright suits.
If he retires one day and is unable to hand over his site to someone worthy that is a different matter. There is always Wayback Machine though. (I say that partially in jest. Clearly you want well-maintained, up-to-date information when it comes to clinical medicine!)
It will be a sorry day for people who suffer from dizziness when Dr Hain retires. He really has a wealth of knowledge and a total dedication to his chosen field which seems lacking elsewhere. I’ve noticed his regular updates and modification dates and that often he rewrites sections presumably as a result of more recent experience. I really appreciated that, following the upgrade, the article on preventatives is very much more concise but so much easier to follow than before. Whenever I use his website I’m amazed at its very existence and wonder at the hours involved in the creation of so many articles. I think it is a priceless resource. Personally it has proved a lifeline to me. I was in no way criticising his actions, just a throw away comment agreeing with @dizzy3 that some articles familiar to us appear to have disappeared. I guess some have been incorporated elsewhere. I suspect some have been updated and extended to incorporate new material to such an extent as to seem unrecognisable . Until I can either find a note of or remember the title of the actual article I couldn’t locate and assumed it had been taken down I cannot be exactly sure into which category it falls.