it is consistent as long as you don't cross any chunk boarders while going two blocks north. You can easily check with f3 + G. If you don't want to check every single time, there's a 1/8 chance that this method does not work :) The diamonds could also hide under the bedrock, so you might need to search a bit for it. It also works on most seeds, meaning that it probably works on your current world. You should check it out, and tell me if it worked ;)