I was reading this comment thread and two comments put up a good point that, if properties of a topic are changed by a moderator, then some of those comments lose their context and can create confusion for newcomers to the discussion.
A relatively simple solution to this problem would be to mark each comment submitted prior to the changing of a topic's properties with some sort of icon, similar to how the OP of a topic has (OP) next to their username.
As for what that icon would be, or even if the signifier would be an icon at all, isn't something I've put a lot of thought in to. Something as simple as one of the Unicode hourglass icons would be fine, and offer some contextual clues. Hovering over the icon with a mouse cursor could reveal text explaining that the comment was made prior to changes.
Or, we could just include a message next to the usernames of comments, similar to how the date is included.
What changes to a topic should trigger this signifier on comments? I feel like editing the linked URL is an obvious one, but editing the title or tags is less likely to take context away from some comments, so maybe they shouldn't trigger anything.
Of course, just looking at the topic log and comparing that to when a comment was made would be investigative enough to come to your own conclusion, but that requires effort.