Don't count on them being correct. In Massachusetts, we call DigSafe, who calls Verizon. Verizon outsources to "IDM" who then outsources to "On Target". I happen to know that my phone line is buried, so when they marked it as 'NO buried phone line' I knew it was wrong.
I also later got a survey from verizon about it - but when I click on the link for the survey it says it cannot process it.