How to manage multiple engine version and templates?

I have 2 different versions of the engine installed side by side (4.2.1 and 4.3.1).

On the “Library” tab of the launcher it shows all installed templates with their corresponding versions:

On the Marketplace tab however, it shows me that most of the available content is not installed.

I don’t understand if i have to re-download all the content from the marketplace with every version i upgrade? what is the version number of the downloaded templates used for ?

I’m guessing if you downloaded them before the Vault system appeared the launcher dont see them as downloaded. But if you already have them you dont need to worry about it really. You can always manually duplicate them and then open them with whichever engine version you like.

I am worrying about disk space, as i seem to have multiple copies of each project

Then you can move them to another HDD. I have a 120GB SSD and a 1TB HDD, so i move all of the Marketplace projects to the HDD. After you move them open them once and they will appear in the library again. Also you can delete the older versions of the projects if you have multiple copies of the same marketplace content, and leave only the one that is opened with the latest version of the engine.