That's quite possible. I had not realized that the downvote option disappeared so quickly. I think my karma accrued overnight, so when I noticed I'd exceeded

That's quite possible. I had not realized that the downvote option disappeared so quickly. I think my karma accrued overnight, so when I noticed I'd exceeded the threshold a lot of the thread was perhaps a day old. The only thing I am relatively certain of is that some of the older comments in the thread were not downvotable, and the newer ones were.