The ones that you can edit are more recent that the ones that you cannot.
I find that ability to edit expires after a certain time on forum posts, which may be reasonable in general. Presumably the same rule is being applied to documentation, which is not so great.
If your analysis is correct, then than that would mean posts are no longer editable after 1 month, roughly. Whether that’s reasonable, in general, I find debatable - at least users should be able to delete posts if they want to - no questions asked.
Perhaps @slimy can confirm, or not, if the hypothesis is correct.
And, then I agree, as far as posts in the Documentaiton category should be editable perpetuity.
@uckelman is there any way you can change the edit timeout or curfew? At least for the Documentation category? That is, if that is indeed the problem.
Just a thought: I’ve been able to edit Documentation Index even though it is a relatively old post. So perhaps the edit curfew depends on the user-level of the creator of the post?
This was news to me too, or I had forgotten. Turns out there is a hidden option at the foot of the post. Maybe it is more obvious when creating a post in the first place.