I didn't even know about the earliest ch1 code lol. Is it too late to start entering them? I've met Melisandre and started on Elsa. What codes should I even enter? Looks like there's a lot of overlapping codes on the first page.
First of all, it is not late, like yes you should have entered the code earlier, but I think it is OK.
Second, the latest code is "SNOW_QUEEN", put it in as is without the quotation.
Edit: I think because you have put the code late that there might be some stuff that you will miss, and I recommend that you start over, but it is up to you.