How to add a register or not

First of all, sorry about my limited english.

I apologize if this topic was previously discussed, but I could not find it in the forum.

My problem is the following:

A common table of articles that has the following fields:

art_id / art_cod / art_desc / art_stk / art_res_cant / art_res_to_date

Id, code, description, stock, reserved quantity, reserved to date

If the reserved quantity is equal to the stock, there is no problem, because the stock remains at zero until the reservation date. And so it is recorded in the registry.

But if the reserved amount is less than the stock, I must leave the record with the reserved amount and add a new record with the stock minus that amount

I started doing it in the list form, I tried to make a custom view, but I can not find the best way.

Some help?