I too have created a document that details what I hope is everything, from descriptions of insurance policies to bank accounts to digital assets. All of the “secure” information is in 1Password, and my master password is in a note in a shared vault in 1PW which my daughter can access. All contact information is referenced in the document and all contacts are, of course, in Contacts.
Maintaining access to old data is hard and does require a periodic updating. Years ago I had things backed up to CD, then DVDs, now external drives, and servers, and the cloud. As storage media become obsolete you do need to migrate your data, and if you are storing on hard drives, periodically spin up the drives to ensure they still function.
A possibly harder question is the format in which to store data. The Library of Congress has a document on preferred data formats for various types of data, which can be a somewhat helpful guide.
I try to keep things in formats that I expect will stand the test of time, at least for the relevant time for me, such as plain text files and PDFs, but you never know what the future will bring. Some things are very hard to put into such formats. For example, video formats change and evolve, but I don’t know of a way to convert our old family movies (now in .MOV files, after surviving conversion from 16mm film (from the 1960’s through 1970’s) to VHS tape, to digitization by feeding the video through an old camcorder which output a digital stream on FireWire into a Linux box in the 90s… to something “permanent” like plain text! What of Numbers spreadsheets if Apple changes the format for Numbers files down the line and you don’t run through your old files and update them?
I have files I can access that are over 30 years old as well, but some code that I wrote in the 90s in for a research project would be great to be able to look at today, but it was written in some early version of Visual Basic that I am sure no longer exists and so the files are a mishmash of data and code that is virtually uninterpretable, even if the files themselves survive.