I have 4.12 or something like that on my PC upstairs, and have already done some things in it, will those projects still work in more recent versions of UR? (it’s two updates behind)
You can indeed use your 4.12 project in a more recent version of Unreal however you will need to use the upgrade feature to make it into, for example, a 4.14 project.
When you attempt to open your project in a newer version of Unreal the editor will remind you that your project is from an older version and ask if you’re okay with updating it.
Once that is complete your project will now be marked as a 4.14 project instead of a 4.12 project and be useable in the 4.14 editor.
Keep in mind that although compatibility is often kept between versions, occasionally something may be different enough that a few manual tweaks/fixes will be needed.
I suggest having a backup of your project or when prompted to upgrade your project selecting “Upgrade as Copy”.