The official MS stance is that W10 is still free for people with accessibility needs. But there’s no policing of that at all, you can just download and install it.
I think that ended at the start of the year.
I have a (only slightly) better than a layman’s knowledge of MS Licensing, but in short if the license works then you’re free and clear – doesn’t mean it’s in line with their licensing rules or indeed the law (which are sometimes contradictory) but MS license codes are one-use, as in you use it, if MS severs accept it then they assign an allowance to the device, they’re not transferable, but the code ceases to exist once activated so as long as it works, you’re fine.
If audited they’ll only be looking for OSs that show you they’re activated, not codes as such as they haven’t produced license stickers for years.