Yeah, I'm almost certain they were added in retroactively. I actually thought the original Nov 22nd comic was a bit odd, when it first appeared. Both the "first comic in history to go back in time" statement, because surely other webcomics had done flashbacks before (I thought it was going to be a regular flashback, at that time). And the fact that it said "come back tomorrow", and then the comic promptly went on hiatus for almost a month, but I figured that these things happen, for personal reasons or whatever. I saw these comics for the first time just now, thanks to your post! I kept regularly checking the front page to see if there was a new update, but it never occurred to me to hit the "previous" button. Now I'm guessing that rather than there being a hiatus, the Nov 17-20 comics were added in at about the same rate as regular updates!
Now that I've read them, I suppose it's actually a nice experiment. You go back one comic and learn about
SPOILERS:the zombie phone call, then you go back another and discover the food poisoning issue, still further back and you figure out how the sandwich got there in the first place, etc.
I thought it was actually a pretty neat way of storytelling, revealing these little bits of info at a time, and it kinda reminded me of the movie Memento in a way.
However, I'd almost reached the point where I was just going to stop checking the CYS site because I was under the impression that there hadn't been any updates for weeks! Then today's comic appeared and I thought ah, nice, CYS is back from hiatus, but it still didn't occur to me to go back in the archives until I came here and read this post. A slightly more obvious hint in that comment under the Nov 22nd comic might have helped. Edited to add
: Upon rereading your post I see you actually also mentioned Memento! Missed that the first time. GMTA