In Alphametic Puzzle #5943, at the checking phase I got "incorrect". I took screenshot and re-entered the numbers to ascertain that I put the right ones there. It turned out that I had made the correct solution, but hadn't put numbers in the inequality at the right. So, would it be wise to have fixed (non-enterable) letters for these? Or else make the check procedure highlight empty places?
I've always thought you should get a different message if the puzzle is incomplete, as opposed to incorrect.
It probably isn't possible for all puzzles, but for the ones where you need to enter something into every cell (for some definition of 'cell'), it would be pretty easy to implement, and very helpful!
Highlighting the missing cells would be a bonus, but not essential.