In this tutorial, we'll be discussing some of the unique aspects of our educational plans. We'll look at the use of accounts and access codes as well as how to...
The maximum time for code validity is 3 months.
In your scenario, you would have to create 4 codes during the year.
Each time you create a new code, you would provide it to the group of students you would be working with for this period only.
Saving projects is done as indicated in this manual article : construct.net/en/make-games/manuals/construct-3/overview/saving-sharing-projects
There is no requirement for a subscription or a code for saving projects.
Projects are saved on your own computer space or a cloud service of your choice.
Cloud service would require accounts on their service, but this is outside of the scope of Construct itself.
Saving : construct.net/en/make-games/manuals/construct-3/overview/saving-projects
Sharing : construct.net/en/make-games/manuals/construct-3/overview/sharing-projects