Proved in what sense? Are you saying that because the internet and digital data hasn't been around for multiple generations, we don't know that it is up to the task of storing data for the long term?
It's certainly proven that digital data can survive moving from one storage media to another (such as when the first becomes obsolete), and can be protected by redundancy, and so on.
> the internet and digital data hasn't been around for multiple generations
The internet has been around for more than 25 years (which is what we commonly refer to as "a generation"), and digital data has been around for almost 50 years now.
It is patently obvious that we've done a very poor job of preserving digital data and internet artefacts, and little is changing. Sure, in theory preservation can be done, but in practice the required effort, cost (in both time, manpower and materials), lack of skills and the breakneck speed of technological change, are impeding most long-term preservation efforts. Even when all planets align, we often find that our tools are not as reliable as we thought (like CDs decaying and becoming unreadable).
The loss rate for analog media is still extremely good. I can read loads of books from the '90s in their original editions with moderate effort, while most of the '90s (and even '00s) internet was literally wiped out. That is a huge problem, and archive.org on its own is not the answer.
It's certainly proven that digital data can survive moving from one storage media to another (such as when the first becomes obsolete), and can be protected by redundancy, and so on.