So for now I will just relax on it and maybe get him a file or box to put all the incomplete projects into.
I love that idea! Even if he never goes in again - what a great keepsake! When he comes to you to worry that his future 4 year old isn't doing whatever, you can pull out the box and show him what he was doing /not doing at that age!
If the school isn't complaining, then I would just let the matter drop. If the tasks are really 'poor fit' I might ask if they can be improved a bit.
Somehow this is reminding me of a poster I saw the bathroom of an administrators office. A toddler leaning over on his junior potty. The caption read: The job isn't complete until the paper work is done!
Perhaps by teaching your son to file his projects when they no longer interest him, you ARE teaching him to 'finish' the job by filing them.
Smiles,
Grinity