Hi Amber & co!
Imagine this: I have a recurring task every Tuesday. I actually did it on Wednesday. But, forgetful as I am, I only realize on Thursday that I still need to check it off. I’m then forced to choose between 'I did it today (= Thursday)' or 'I did it Tuesday.' There’s a day missing!
I’m not really into habit tracking myself, but I can imagine this really messes things up for the habit-tracking crowd!