The code in the Guitar is probably not "1225".
HEAR ME OUT. HEAR ME OUT.
I think it's longer than just 1225.
The way the narrative actually treats it, we haven't yet gotten the code in the guitar. While we saw the first 3 digits as 1 2 2, Kris tears us out before we can finish it, and then there's the entire holiday manor SOUL sequence in which we struggle with Kris over the guitar, and then Carol shows up and ruins everything.
Susie then goes on a long speech about how everything was going perfect until Carol showed up and then emphasizes:
That we will have to make another attempt on the Guitar Code tomorrow.
This is re-emphasized later on if you inspect the shelter:
We know where one of the codes *is* but not its actual value. At least in the eyes of the story, we did not successfully retrieve the code hidden in the guitar. We will have to try again later in the story.
But when discussing this with others, I commonly got a reply to the degree of:
" But we already know the code inside the guitar, it's 1225! Why would we waste time going back to get it when we already know it! "
And to an extent I get that. But I would like to propose something:
The code isn't 1225. At least, not completely. Consider this: If the code were just 1225, wouldn't... wouldn't Susie just be able to memorize that? It's 4 digits, it surely wouldn't be that hard. And look at what she actually says:
Not, "I couldn't really make it out", or, like, "I forgot it", but, she "didn't get to write it down". That to me seems like specific phrasing. You wouldn't need to write down a code that's only 4 digits, would you? Maybe at some point to keep it safe, but, in the moment? Susie's... Well, Susie is Susie, but surely she's not that stupid.
I refuse to believe Susie would see "1225" and go "Oh, shit, it's the code! I need a pen and paper right now, there's no way I can memorize this for a few minutes."
And so I propose a solution: It's not just 1225. It's 1225 plus some additional numbers- potentially a year? Probably the year Dess went missing. That could add up to 4 additional numbers, making it an 8 digit code, making it more reasonable that Susie would feel a need to write it down.
Potentially foreshadowing for this also exists. Remember this scene?
The joke here is literally that there's a "code" that seems to only have 4 inputs at first, Susie literally suggests memorizing it, but then it's revealed that it's too long to memorize and must be written down, pen on paper.
Feels like it could be foreshadowing to me.
TLDR: I think the code in the guitar is an 8-digit code, not a 4-digit code, thus solidifying the idea that Yes, we Do have to go back for the Guitar.