Paperwork is nice, but there is no way it is super important as long as you can verify a positive history on the bikes origins. IE, not stolen. Get a bill of sale with description.
My bike has had a few different cases and I've even swapped frames over the years so there's no friggin way numbers will match. However I've for titles for any frame I've had.
On the motor, look at compression, ease of start, plug condition(rich/lean, detonation, etc) , pull the dip stick to see if the bottom end is taken care of, maybe drop the carb bowls, check coolant level.
Chassis, listen for squeaks and creaks, any loose wobbly stuff, wonky bearings, etc. Things should be moderately clean and wiring should be tidy.