This is sufficient because:

The original page is explicitly Drupal 7 documentation.
Drupal 7 reached end of life on January 5, 2025.
Most of its tools, APIs, modules, screen readers, conference links, and external resources are obsolete or dead.
Its useful subjects already have maintained replacements in the current accessibility guide.
Updating the resource list would create a second list that would immediately begin drifting from the current External Accessibility Resources page.
Retaining the original content below a warning would still expose unsupported PHP examples, WCAG 1.0 material, and obsolete product recommendations to search visitors.
The short pointer preserves the historical URL while moving readers to supported documentation.

The old body should be removed, not retained beneath the notice.