Question:
Sacramento to willows ca to pick up preload.
Load is going willows ca to salt lake city ut. Pick up paperwork and look for trailer in yard. Trailer not in yard, shipper agrees trailer was loaded. Check filed bills of ladling. Can not read signature, but has other company drivers truck number.
6 Year driver new to company dropped off empty trailer, came back only loaded trailer he saw. Hooked to it, took bills out cubby hole signed them, noticed BOL trailer number did not match his hooked to trailer, thought shipper made mistake, and took off driving to south dakota. Saturday morning shipper not around 0500hrs and driver did not think to ask dispatch BOL and trailer did not match.
All ended well. Both loaded trailers were going thru salt lake city ut. Driver dropped trailer in salt lake city yard. And I drove the south dakota trailer to SLC UT, and turned it over to a team.
Punch line is it was a saturday night and trying to get a hold of anyone to straighen it out.
On preloads check your BOL bill of ladling for correct trailer number and seal number. Oh yeah make sure the address on the BOL is where you are headed. Was at place in kalifornia where the shipper holds up the bol and reads the address to you. If paperwork trl number and hooked to do not match, ask shipper, dispatch whats up.
Would been a hoot if trailers had been going in opposite directions.

Answer:
Check that paperwork. ALWAYS check that paperwork regardless if it is preloaded or live loaded.
Also speaking of paperwork. Do yourselves a big favour. NEVER go into someplace to deliver and not have 2 copies of the bills. Also if you are dropping a loaded trailer someplace for relay be courtious and leave 2 copies of the bills with the load for the next driver. You may need to spend a 50 cents or a dollar and a few minutes at a stop to make those copies (if the shipper is unable or unwilling to give you an extra set) but it will save you headaches in the long run.
I will always be a mutter trucker at heart.