You can definitely order addressed cards and non-addressed cards in the same order.
When you go to personalize and choose an envelope, you'll be prompted to pick a style, add the return address and then choose recipients. Once you have chosen recipients, you will be taken to your cart.
In your cart you will see two quantities: Addressed and Non-Addressed. Addressed will always match the number of recipients you chose. Non-Addressed will be the amount of cards with either blank or return address only envelopes. This can be updated in quantities of 10 using the drop-down. These quantities together will be your total number of cards.
If you have further questions, please contact us and our support team will be happy to assist!