Lots of posts around this topic, but none on the money I can find - but I may be wrong.
So I completed the set of tablets (10, 8 and 7) today and bought a "new" 7 off ebay having checked "nothing has been activated on it." What the crazy fool didn't tell me was they had turned it on shortly after purchase in June and let it upgrade to Win 10 - BEFORE they had activated office. So I now have the Win 8 recovery partition (have accessed it and copied to another PC so I can see all the files) and a Win 10 recovery. Of course, resetting now goes back to Win 10.
But, I would very much like the office product key! "Get office" on the Win 10 machine just offers me the chance to buy, unlike my 8 and 10 tablets that both took me through getting my free year.
If there are way to access the unused product key from the original recovery partition without the various tricks needed to persuade the device to recover itself to Win 8.1. I was hoping it was just hidden away inside an xml file, but I have trawled through every one on the recovery partition with no luck.