Hi Dominique,
I'm afraid your description of what happens in the use case you describe is wrong. I have just tested the following scenario (in current Moodle 2.7 version) and here are my findings.
1.- Create 3 MCQ questions. For each question, in the Multiple tries section, enter Hint texts in the Hint 1 and Hint 2 boxes and leave the "Penalty for each incorrect try" at its default 33.333% value.
2.- Create a Quiz using those 3 MCQ questions, each on its own page. Quiz settings: How questions behave -> Interactive with multiple tries. Quiz setting Layout / Navigation method: Sequential.
3.- Logged in as student, take the quiz.
a) Page 1, MCQ Question 1. Select a wrong choice. Click the Check button. Feedback messages zone displays: "Your answer is incorrect", Hint 1 text and the Try again button. Click Try again. Now select the correct choice. Cick the Check button. Feedback zone displays "Your answer is correct.". And the grey navigation zone on the left of the question also displays "Correct". Click Next.
b) Page 2, MCQ Question 2. Select a wrong choice. Click the Check button. Feedback messages zone displays: "Your answer is incorrect", the Hint 1 text and the Try again button. Click Try again. Now select the correct choice. Do not click the Try again button. Click Next.
c) Page 3, MCQ Question 3. Select the correct choice. Do not click the Try again button. Click Next.
4.- On the Summary of attempt page you see:
Question Status
1 Correct
2 Tries remaining: 2
3 Tries remaining: 3
This display is misleading, as I pointed out in this other discussion. Questions 2 and 3 ought to be marked as "Correct".
5.- Click the "Submit all and finish" button. Now you'll see that all your correct responses have been saved and scored regardless of the student having checked them with the "Try again" button. For Q1 and Q2 you only get 0.67 out of 1 because of the 0.33% penalty for one wrong try. For Q3 you get full marks.
I hope you are re-assured that the quiz works as expected in this respect, and that your students cannot complain that they were not credited for a correct answer by clicking the Next button too soon.
Joseph