Just google your windows 7 ultimate key and you'll know if you have genuine copy or no. If google will show websites with that key it is not genuine. To be fair COA is only proof (except new computers with windows 8, because key is saved in bios)
I don't really need to Google the key as I already know it's genuine (I Googled it anyway and it came up with nothing as expected). I can always remove Windows 7 as I know some people won't be comfortable without the COA.