The way you organize stocks now seems a little out dated and when you have a lot of stocks it can be confusing to use.
I'm suggesting the following.

When you want to stack stocks, have an option to choose which ones to stack. If you have 4-5 different investments in one stock this can be very useful, or if you want to keep stock investments separate from benefits.
The way I suggest doing this is by adding a little check box next to where stack is and you click the box for the stocks you wish to stack. ONLY the checked boxes will be stacked.




Each stock be organized by group, not by date.
For example:

Each PRN stock that you own will be grouped together

I did a "rough" sketch of what I am suggesting.
The stocks are grouped together, regardless of days, and there is a little check box so you can check the boxes you want to stack, then click stack to stack exactly the stocks you want.