My as-built showed the correct tank and distribution box locations, but showed the field as a single line running 40' straight out. It even showed the wrong driveway location (front vs. actual end garage door).
My system was failing, and when they started checking, the d-box was worn out (concrete eaten through by microbial action at the air-water line after 30 years, apparently a common problem). It had two lines coming out, both parallel to the house, 9 feet apart. One had settled over time and was actually angled slightly uphill, so in effect I only had one 19' line.
Not a month earlier I had had a cement truck on the lawn just short of it (did not cause settling, wrong end). There is also an electric line run over it, because we were trying to avoid the system as marked on the as-built when we had it installed.
They replaced the box, ran an enzyme solution to break up the grease in the field, and added a 3rd line straight out.
My wife wants a pool, and had the surveyors from the pool company come out. They checked the town for the files...the septic company didn't file a new as-built for the location corrections and added line.
We are also a title-V state, where septics must be inspected, including d-boxes, before property can change hands. If they had inspected the box, they should have at least seen that there were two lines out and not one as in the town records when they pulled the cover.
All this to say: take any as-builts with a very large grain of salt.