Long term data storage

How should one store data for the long term? With, for example, optical media deteriorating over 15 years, magnetic storage losing polarity over decades, cloud services going out of business and the inevitable changes in technology, it is not surprising that retaining information and cherished memories for future generations is greatly discussed. I am no IT expert and merely note the accepted wisdom of making sure that data is backed up in different methods and different formats, coupled with this being an iterative process over time to avoid obsolescence issues. However last month I visited Lincoln Castle and saw their 1215 copy of the Magna Carta. Eight hundred years old and perfectly legible (in Latin), could this example of long term storage be of assistance? Calf vellum and oak gall ink being the storage media. For those interested in taking this further, to make vellum first catch your animal, to make oak gall ink first plant an acorn.