Here's a really old ISBN, which I picked at random because I wrote the book (often also a random process at times) -- almost 25 years ago: 978-0782120813 I ha

Here's a really old ISBN, which I picked at random because I wrote the book (often also a random process at times) -- almost 25 years ago: 978-0782120813 I had no trouble finding the book via this magic number. I don't know how that compares to a 25 year old DOI for an item that was in limited publication. (shameless plug, fair, but it's an example for which I happen to know the provenance of the isbn, even before publication, and I also have an idea at how obscure this item turned out to be after public distribution.)