Doug's story of getting his internet fixed (possibly) reminded me to update this thread.

I had a cabling company come out to the site yesterday to test the ethernet lines running under the ground through the conduit. This is something I can't do as they have the fancy $8000 device for this purpose. Well, the cables passed the first test when it found the pins all lined up, but then while it was checking for consistency in the line, one of the techs pointed out the distance reading on the device:

441 feet

Clearly the problem had been found. This raises a couple questions for me, the primary one being how it ever worked (for two years) to begin with! I'm also wondering why nobody who was putting in the cable had questioned how much cable was being laid out.

The cabling guys were also dismayed that the end of the conduit had been filled with concrete, by the way. They had no explanation for that.

So I've arranged an appointment for the fiber termination and ordered the converters. Hopefully this will all be fixed by Monday!