Re: The debris can't actually be in a geosynchronous orbit
Not true. Geostationary satellites have to perform station-keeping manouevres to maintain their figure-8 box. Older satellites are often allowed to develop inclined orbits, which from the ground appear to oscillate above and below the equator. This saves fuel but can be tracked by suitable ground stations, and allows the satellites to communicate with ground stations in polar latitudes which are usually out of sight. Such debris would periodically cross the bounding box of a satellite on station at GEO.
Any event which creates debris is also likely to impart energy which would cause the debris to drift east or west around GEO, potentially affecting other orbital positions. Look up Galaxy 15, a rogue Intelsat bird which drifted around the belt for several months in 2010: https://en.wikipedia.org/wiki/Galaxy_15.