Just to clarify the white spaces in question are the unused channels, not the gaps between channels. I believe each channel has a protective space before and after it called a guard band. I think there is a possibility for interference if these guard bands were to be used. However, unused channels in a give geographical region would definitely not interfere with existing commercial signals.
The example you gave where channel 4 in your area might be located in a different piece of spectrum was a bad one. As a correction, consider that the NYC area has operators using channel 7 and 9. While the DC metro area uses Channels 7 and 8. In NYC channel 8 could be used for white space applications, but in DC it would interfere with our local New Channel 8. The inverse is the same for channel 9, which could be used in DC, but not in NYC.
Thanks for the info on this. I was completely unaware of the issue and now I’m seeking to get educated quickly.