I need help with resources for older versions (up to 1.7.2) and getting those versions to run properly through the launcher I'm developing.

Hi everyone, I’m developing my own Minecraft launcher in my spare time. Right now, I’m having trouble launching legacy versions up to 1.6 and there’s no sound in the game up to 1.7.2. I read online that older versions use a different asset structure. But that doesn’t make sense since the textures are in place. I’d appreciate it if someone could explain how to properly work with legacy versions.

For those interested, here is the repository - https://github.com/MenshovAnton/CubeXLauncher