Good point. Most 35mm prints will be a true 4K resolution if they did a 4K scan.
So if they say it is a 4K scan of 35mm print - the it will truly be 4K resolution.
Your 4K TV will do an upconvert on the 2K blu ray that will be as good as the online digital 4K version (that itself is just an upconvert).
i would only look towards the digital 4K version if it had an HDR/DV pass that was noteworthy.