Quick answer
The Steam achievement list requires reading all 61 text logs. That official total is used here even when community route counts differ.
Confirmed target
Steam's achievement wording supplies the clearest fixed target: read all 61 text logs. Community walkthroughs sometimes organize the same material by terminals, mailboxes, or chapter, which can make intermediate counts look different.
Tracking advice
Open each readable entry rather than only interacting with the terminal. Finish reading before leaving the interface, then mark it in your own chapter notes. If a community checklist and the in-game achievement counter disagree, treat the official achievement total as the authority and revisit entries that were opened but not fully registered.