How do I calculate for hidden date ?

I had been suffering from this problem for several days.
No matter how many times I looked at what was wrong with the code I wrote, I couldn't figure it out.

Finaly I noticed the following problem.

I kept a number of different dates (more precisely, the history of initialized dates and dates updated in the past) in hidden fields to calculate the dates to display in the form.

It's not that my code was wrong, it's just not really working.

I created a sample form to make this problem easier to understand.

Please see the attachiment PDF.

Is this a bug? Or is it a specification ?

Please let me know if there is another good way.