There's a bit of an edge case here - I have submitted a project, "ClassicZoo". The Amiga port has technically only been in development since December, which would meet within the rules. However, since I'm the person responsible for the original reverse-engineering of ZZT's source code in March 2020 and most of the bugfixes/updates beyond, it could be argued that my personal involvement in the codebase stretches far before the jam's start date. On the other hand, the jam's rules state that using existing source code is allowed... I'll leave judgement to you on that one.