Did it ever occur to you that the coordinates for some of these towers might actually be incorrectly documented in the lookup database. If so, then the location overlay to the map will be wrong. Remember that each tower has a unique identifier along with a lat/lon and that's what Google uses to overlay it's location on the map. If that was noted incorrectly by the carrier or owner of the tower or whoever manages that info then the location on the map will be wrong. Just FYI.