Microsoft Office 365 small business premium activation

I have a copy of Microsoft Office 365 Small Business Premium which up until earlier today was in a sealed box never opened. I went to add this to my Office 365 business tenant using the product key card and got the message "You cannot redeem this product key based on the subscriptions you currently have." 
My tenant currently has Office 365 Business Premium subscriptions which last year were renamed to Microsoft 365 Business Standard.

Do these older retail boxed copies of Office 365 have an expiry date? I can't see any expiry date on the box so assume these should always work. Is there a place I can get support to confirm the status of the product key?