I checked again, and also to my surprise I see that for Office we even offer VL customer the old 2010 media:
However, this does not mean that Microsoft is required to supply a media or key for this old version. you have the right to use Office 2003 with that. In the Product Terms you can read (Universal Terms section) that downgrade rights are supplied without any restriction on the version - e.g. for Office 2019 obtained via Open License, the product terms do apply:
The refernece for the downgrade rights are the licensing terms.
