“why people organized “data” before digital methods”

Reasoning is the most sought and least annotated thing.

I think a good place to start might be with the ISIS Current Bibliography, which has been going strong for a century. Stephen Weldon in Oklahoma is currently leading a very interesting project to integrate all previous organizational schemes into a shared database: cas.ou.edu/stephen-weldon

The idea being that users can look at the collected bibliography through any of these older arrangements, or they can create their own scheme by adjusting various fields and saving it. One corpora, many ways to see it.