Variable products with many options

Hello,
I have some products with a lot of options/variations.
I only created 9 “size” variations in the products admin page with the others options not specified.
When I add a specific size with some option in my quote and I change some options to add a product with the same size but different options, it says that the product is already in the list.
How can I make the button available each time I change one option, and not only when I change the size option ?
Thank you in advance,

Mathilde