That would easily explain comments coming back that were hours old or even days old, but it's extremely unlikely to explain comments coming back that were months or years old, as others in this thread have found.

No database shard would ever have been left that far out of date due to high load.

The only Hanlon's razor I can imagine here is somebody wrote a query to try to undelete something small (intending a single user or something) and forgot the WHERE clause and started to undelete everything. And didn't realize until the query had been executing for several minutes.

Yikes.

(I do actually think this is the most likely, not because of spez's motivations, but because there's zero benefit for Reddit here. It might make sense for them to force subreddits back to public, but undeleting old comments has no strategic value right now.)