A third of six-year-old links are dead, which is normal and fixable
The problem
About a third of links from 2019 no longer resolve. That is typical and it means a third of that year's sourcing is unverifiable.
What is done now
Every external link is submitted to a web archive when a piece is published, and the archived version is linked beside the live one.
The backfill
Working backwards through the archive at about a year a month. 2021 onward is done and 2019 and 2020 are partly recoverable.
