I guess the way I think of it is, you know how you're allowed to use a genre-specific engine, like the RPG Maker series?  You should be allowed to reuse code if it's effectively the kind of thing that an engine like that would do.  I'm not an authority, but that's how I interpret it.  Also the rules are intentionally pretty woggly, and as long as you report it in the "i started early" section, I'm sure a lot of people would forgive you for fudging the rules a little.

P.S. Welcome!  ...is what I would say if this wasn't also my first time. :3

i mean i'm not gonna be a huge stickler on this or anything.  mostly it's just, could this code reasonably be used for two games?  if it's something you've already written then i don't want to force you to retype it to maintain the purity of the jam or whatever.  but if you're essentially reskinning an existing game then that's not so much in the spirit of a game jam

but even then it's hard to make a hard and fast rule — like i've suggested zdoom as an engine before, and you could do plenty there with just a map, not writing a single line of code

I'm guessing that elements and system that you've made before can be repurposed. I have a random-walk maze generator that I've heavily modified and used in almost all of my games. The text file reader and dialogue systems in my games are also largely reused. I'm guessing that if you want to make a camera game similar to this year's submission with most of the same code but a different main character you'll need to list it in the "started early" section. If you just use the code from your clothing menu and make an RPG game where you can equip different items you probably don't need to mention where parts of the equip menu originally came from.