Studio should display a warning when files/projects created in different version are opened.
Usually, Studio projects and individual SDLXLIFF files are forward and backward compatible, but despite the best efforts, some issues may arise when working with files created in a different version. That's why it's good to use the same version through all stages. The thing is there's no easy way to know from which Studio version files originate.
The suggested solution is to record Studio version inside the files and compare it with current version when opening. If there is a mismatch Studio should display a warning.
For people who need to often work with mixed version files, there could be an option to just display a small warning in the status bar, so they know about the mismatch but are not annoyed with pop up window every time they open new file/project.