I think that's saying you can't use ripped graphics, music, etc. If it's your own, it's public domain, or you legally have license to use it, it's fair game.
Viewing post in Can we make art and music for our games before the contest?
Right on. Unfortunately, I'm not entirely convinced that's what this statement means. I may be reading too much into it, but just because you own something or have the right to use it, doesn't mean that it's not pre-existing intellectual property. From my understanding of game jams, the idea is to create all aspects of the game within the allotted time period. I understand that this puts a damper on the capabilities of one person / very small teams and I honestly dislike mentioning this subject at all. I believe the point of a jam is the challenge presented by the time frame, otherwise, why have a time frame at all? If the jam was for fun or no prizes were at stake, I would leave the issue uncontested; however, since this jam doesn't fit that criteria, I can't help but feel that it's unfair for my team to have worked so hard on our product under the time constraints, only to have it judged against products created over the course of days, weeks, or even months. AGAIN, I REALLY dislike bringing this up as it can seem a bit harsh and I apologize if I have "read too much into" the rules. At the end of the day, I'm seeking a fair competition between individuals / groups who's products can be rated against one another on an even keel with consideration to the size of the team involved.
I totally get where you're coming from, it would certainly be cool to see what people come up with creating everything literally from scratch. But, that's not how it is and it sounds like you're putting a constraint on yourself that's unnecessary since it's not one of the rules.
I doubt any of these games were created weeks or months in advance aside from the one that was submitted to the last jam that CT hosted, but a general ground rule I've seen is that you can use pre existing art and code for your project, the caveat is that you don't know the theme prior. If your pre work doesn't match the theme, then you need to redo it, so it's to your advantage to wait.