what if you lack the fragments needed to reverse engineer/reconstruct a means to access the information?

In this case the "Fragment" isnt even a fragment, it would be a completely intact start to finish monstrous amount of data.

The larger the "fragment" is, and more complete it is, the more trivial it becomes to decode it.

And since this data is being purposefully stored in a manner intended for future use, it's very likely it will be encoded in a manner to facilitate and make it as easy as possible to decode in an intuitive manner.

Id strongly suspect every individual "glass" would have some form of "clue" or "how to" at the start of it, that serves as a guide to help the consumer know they are decoding it right.

Off the top of my head one example would be encoding a bunch of digits of the Fibonacci Sequence at the start as character literals (so text form), which even in binary form when inspected physically with a microscope, any scientist would go "oh hey thats Fibonacci!"

Then after that a large blank, followed by perhaps in order the entire ANSI character set from 0 to whatever it goes to now. Or perhaps Unicode.

The whole thing is only like a megabyte or two, so it would be less than 0.1% of the storage data, but having those 2 items at the start of every disk would be an easy way for the consumer to sanity check they are "reading" the data right, and clue them into "yo there's data stored on here" very fast