A similar issue exists with Rush. There are 2 "Coming Soon" achievements that don't exist, and "Santa's Little Helper," which has been around on the Steam site for more than six months, isn't on the list.
There's a lot of games with this issue, unfortunately the mod team is not able to delete achievements. I don't really know what the situation is on the staff's end but I suspect if they were to delete these achievements, they would have to do it by going into the database and removing them manually. I do wonder if we could send a list of achievements Dave's way which need deleting, but the engineers probably have lots of work right now that's far more high priority than cleaning false achievements out of the database.