I have bought a few assets recently then learned I can’t use them on 4.11 and I don’t have them in main project. I have found out that a bug with 4.11 is likely not going to be resolved until the next editor update and that’s bad news because I now plan to avoid updates for a few weeks so I can actually use assets. All of the other assets I would consider purchasing right now are also not available, which is OK with me if Epic Games would make it easier to revert to older versions.
If you are looking for the source code for the 4.10 version of the Engine, all you need to do is click the Branch drop-down and select the Tags tab. This will provide you with a list containing a snapshot of the source code at the point where every version preview and release has taken place.