I do own Kingdom Come Deliverance and all 5 DLCs of Kingdom Come Deliverance. Yet on the Page there is an Option to "Buy all games in the series. If you already own a game from the series, it won’t be added to your cart.".
If I click that I can pay 18€ for the "Kingdom Come: Deliverance - Royal DLC Package" which contains all 5 DLS, but I already own them all. So you make me pay 18€ for something that I already own, even though you promise things I already own would not be added to the cart.
That is not nice to say the least and it might be close to being fraudulent.
Please find a way around that, maybe give everybody who owns all 5 addons this Royal DLC Package automatically.