The continued free (except for all the time you spend) upgrade to Windows 10 operates in Microsoft's own selfish interest to proselytize everything Microsoft like the Microsoft Store, Bing, Office 365, the Microsoft cloud, etc etc. With all this stuff to sell people and a vehicle to do it better than any other Windows, why not the free upgrade to Windows 10? If Microsoft pulled to plug in the free upgrade, they would be shooting themselves in their feet. Satya Nadella is smart enough to have figured this out. The free-upgrade-within-the-first-year was simply another, but less lame, ploy to get everybody racing to Windows 10.
Here is what I have found out installing Windows 10 many times over:
You have a Windows 7 Home product key, so you can upgrade to Windows 10 Home.
You have a Windows 7 Pro product key, so you can upgrade to Windows 10 Pro.
Ditto for Windows 8.
If you have a Windows 8 or 8.1 system without a product key sticker, by arrangement between the name-brand manufacturer and Microsoft burns product key info into the BIOS. So when you upgrade one of these computers, the Windows 10 install ISO picks the right version of Windows 10 and activates it automatically.
I have no idea if, when and how to upgrade Windows 7 Starter or Windows 7 Ultimate. I do not see these versions very often at all.