See, now, the way I have done it in the past is exactly what the builder did. I put wires into the ceiling, if that's where my speaker goes, then I measure where the wire is off of the two closest walls and mark it on the drawing. 68" left, 42" down, that's where the wire is. I go to that location, cut in my speaker hole, and the wire is right where the drawings said it was.
This isn't a hunting game.
When wires are properly pulled and then their location is properly indicated, you have an exact map to their location. A good low-voltage guy will leave 5 or 10 feet extra of wire in the ceiling so that the wire can be relocated several feet away if desired. No harm in the extra cable being there.
My question would be why anyone would pull wire to a ceiling if the intent was not to use ceiling speakers. If ceiling speakers are going in, then the wire should be pulled to the exact location that the ceiling speakers will go. This should be planned ahead of time, and indicated on the build drawings, or pre-drywall if during construction.
I think I went to my home build every other day to see how things were going. I may have interjected a complaint just once or twice. For things that were in the contract that they had missed. Like a dedicated 20amp circuit under the stairs for A/V. They fixed it politely and caught it pre-drywall.
Now that you have found that the drawings are accurate, if you have more locations you need to find, trust that the installers properly labeled things for you.
I do recommend a stud sensor so you can ensure you aren't cutting right into a joist.