Auburn Hills, MI
since the loop is built (put together via multiple trucks, and splice points) when a dedicated loop is installed, and the line share loop (dial tone) was built when ever it was installed, you could be talking a difference of years, or decades, so it is possible the 2 loops take different routes/trucks to get from the CO to the NID.
As an example, at my house, our line share real world distance is around 14,000 feet, where as my dedicated loop real world distance is 11,000 feet. I have seen some where there is up to a 8-9,000 feet difference, and others then are within a few feet of each other, so every location is different.
Then in other cases you run into issues of the dial-tone being feed by partial fiber (A Remote Terminal, is a good example), so only a dedicated loop service would be possible, since ADSL, needs 100% copper. And some RT's are only for voice, not for voice and DSL, and then you have to factor in Covad only has access to some ILEC RT's. But now were are getting off topic, lol as there are many factors involved in who can/can not do what where.
Lightning Bolt Technologies