That's right! You can infact help Mojang find versions of minecraft that are lost! This tweet by Jeb explains how lost jars can legally be redistributed back to Mojang for public use. https://twitter.com/jeb_/status/915107982958059520
Hey, mods can you pin this post? I'm probably gonna regret making this reply, but i think that this thread is one that might actually affect minecraft, and its history if it's pinned.