[phire]

CPU documentation often lies.

The docs are written by completely different Technical Writing teams, who don't always fully understand the design they are documenting. They are usually correct enough for someone using them normally, but I've learned that relying on manuals to actually understand the underlying implementation (or its history) is problematic.

So reuse of 486 documentation doesn't prove anything. IMO it's more likely that the Technical Writing team saw how close the design was to the 486 and decided to re-use that documentation as the starting point.