Both stocks have serial numbers.
If you're comfortable using a screw driver you can carefully separate the forend wood from the iron to reveal the forend's serial number. The number for the butt is under the trigger guard tang.
Be careful, use appropriate screw driver.
The best way to learn to identify original condition is to look very closely at lots and lots of guns, most preferably in high condition, but look at well used guns also. Pay attention to the tiniest details; you will develop an eye for inconsistencies.
Even experts can be fooled.
I commend your ethical concern in regards to accurately describing your gun.